How chaotic a planet's obliquity is depends on how fast it rotates.
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Although our planet's obliquity is relatively constant, it does change by a mere few degrees.
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Its obliquity nods up and down this way between 19723º and 24.5º regularly every 41,000 years.
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On moonless Mars, things are very different; the obliquity shifts around both more, and more chaotically.
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Take the Moon away, and the Earth's obliquity becomes even less stable than Mars's, swinging as high as 85º.
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So yes, without the Moon, an Earth with 24-hour days would suffer radical chaotic shifts in its obliquity.
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As such, there are several knobs that must be tuned to allow life and, Earth's mild obliquity is one.
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Bishop's withholding is less a matter of Moore-like modernist obliquity, however, than of the guarded reticence that was her legacy and her means of control.
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David Waltham, a British geophysicist, suggests in his book "Lucky Planet", published in 2014, that complex life needs both a pretty stable obliquity and a fairly long day.
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Obliquity has led to greater success in novelizing the sixteenth President than have attempts to see him from the inside out and through his own point of view.
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Dr Waltham argues that the Moon is just the right size to allow the Earth both a stable obliquity and poles warm enough to keep any ice ages relatively minor.
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Over the aeons its obliquity can get as high as 60º—a situation in which inhabitants, if there were any, would experience the midnight sun far into the tropics, producing intolerably hot hyper-seasons.
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Such a slouch, or obliquity, has long caused astronomers to wonder whether Earth's tilt — which you could argue is in a sweet spot between more extreme obliquities — helped create the conditions necessary for life.
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Although the timescale on which such changes would unfold is exceedingly long (tens to hundreds of millions of years), chaotic variation of the Earth's obliquity can prove detrimental to the stability of our climate, and the overall habitability of our planet.
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However, this new research shows that even if a planet seems Earth-like and is orbiting at the right distance from its star, if "its orbit and obliquity oscillate like crazy, another planet might be better for follow-up with telescopes of the future," Deitrick said.
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This new research looked at how a planet&aposs obliquity, or the angle at which a planet&aposs rotation axis tilts, and its orbital eccentricity, a parameter that determines the amount that an orbit deviates from a perfect circle, could affect that planet&aposs potential to be habitable.
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It orbits our own in a lopsided ellipse that keeps it within our view for longer and longer stretches each year, spinning frantically at some unlikely obliquity where the sun only ever crosses the horizon to set, never to rise, and golden hour is forever, and it's always 11 o'clock somewhere.
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Beneficial features that Earth has that are lacking on Mars include a strong magnetic field, a large moon (to provide tides that agitate the ocean's chemistry, and to stabilize the obliquity or tilt of the planet, and hence its seasons), and plate tectonics (to recycle oxygen and other resources back into the ocean crust).
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"We found that planets in the habitable zone could abruptly enter &apossnowball&apos states if the eccentricity or the semi-major axis variations — changes in the distance between a planet and star over an orbit — were large or if the planet&aposs obliquity increased beyond 35 degrees," Russell Deitrick, lead author of the new work and a postdoctoral researcher at the University of Bern who completed this research at UW, said in a statement .
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Planet and a Second Planet Detected via Transit Timing Variations Validation of 12 Small Kepler Transiting Planets in the Habitable Zone Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone VizieR Online Data Catalog: Small Kepler planets radial velocities Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets Two Earth-sized planets orbiting Kepler-20 Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star The Hot-Jupiter Kepler-17b: Discovery, Obliquity from Stroboscopic Starspots, and Atmospheric Characterization 2.
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Astronomers produce new fundamental ephemerides as the accuracy of observation improves and as the understanding of the dynamics increases, and from these ephemerides various astronomical values, including the obliquity, are derived. Obliquity of the ecliptic for 20,000 years, from Laskar (1986). Note that the obliquity varies only from 24.2° to 22.5° during this time. The red point represents the year 2000. Until 1983 the obliquity for any date was calculated from work of Newcomb, who analyzed positions of the planets until about 1895: where is the obliquity and is tropical centuries from B1900.0 to the date in question.
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The tropical arctic zone covers the overlapping regions of the tropical and arctic zones. This unique climatic zone is only possible on objects that have an obliquity range between 45° and 135°. Since the obliquity of Pluto varies between a minimum of 103° and a maximum of 127°, it therefore has a tropical arctic climate zone. This high obliquity implies that most of Pluto's surface experiences both tropical and arctic climates over the 2.8 million year obliquity cycle.
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The Moon has a stabilizing effect on Earth's obliquity. Frequency map analysis conducted in 1993 suggested that, in the absence of the Moon, the obliquity could change rapidly due to orbital resonances and chaotic behavior of the Solar System, reaching as high as 90° in as little as a few million years (also see Orbit of the Moon). However, more recent numerical simulations made in 2011 indicated that even in the absence of the Moon, Earth's obliquity might not be quite so unstable; varying only by about 20–25°. To resolve this contradiction, diffusion rate of obliquity has been calculated, and it was found that it takes more than billions of years for Earth's obliquity to reach near 90°.
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When the tilt is greater (high obliquity), the seasons are more extreme. During times when the tilt is less (low obliquity), the seasons are less extreme. Less tilt also means that the polar regions receive less light from the sun.
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Obliquity of the ecliptic for 20,000 years, from Laskar (1986). The red point represents the year 2000. The exact angular value of the obliquity is found by observation of the motions of Earth and planets over many years. Astronomers produce new fundamental ephemerides as the accuracy of observation improves and as the understanding of the dynamics increases, and from these ephemerides various astronomical values, including the obliquity, are derived.
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The doxographer and theologian Aetius attributes to Pythagoras the exact measurement of the obliquity.
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In either case, the climate around the equator is not affected nearly as much as the higher latitudes, thereby creating a sizable difference in how obliquity affects different latitudes. This is all, of course, dependent on what the actual tilt angle is at any given point in time. The thing is, though, that Earth does in fact change obliquity over time in a cyclic pattern. Earth's obliquity does not change much, though, as obliquity has been determined to cycle between the small range of 22.2 degrees to 24.5 degrees, in a cycle that lasts approximately 41,000 years.
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Modulation of the precession driven insolation cycle is the primary impact of obliquity on the North African Monsoon. Evidence for the impact of obliquity on the intensity of the North African Monsoon has been found in records of dust deposits from ocean cores in the Eastern Mediterranean that occur as a result of Aeolian processes. This evidence requires complex feedback mechanisms to explain since the strongest impact of obliquity on insolation is found in the high latitudes. Two possible mechanisms for the existence of an obliquity tracer found in the Eastern Mediterranean Aeolian dust deposits have been proposed.
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However, recent geologic evidence suggests that FSDs are deposits left by glaciers, which covered portions of the volcanoes during a recent period of high obliquity. During periods of high obliquity (axial tilt) the polar regions receive higher levels of sunlight. More water from the poles enters the atmosphere and condenses as ice or snowfall in the cooler equatorial regions. Mars changes its obliquity from about 15° to 35° in cycles of 120,000 years.
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Legend says that "Awang Koubru Asuppa" has notion of origin and obliquity of earth and planets.
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Using numerical methods to simulate Solar System behavior, long-term changes in Earth's orbit, and hence its obliquity, have been investigated over a period of several million years. For the past 5 million years, Earth's obliquity has varied between and , with a mean period of 41,040 years. This cycle is a combination of precession and the largest term in the motion of the ecliptic. For the next 1 million years, the cycle will carry the obliquity between and .
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In directions other than the normal to the primary wavefront, the secondary waves were weakened due to obliquity, but weakened much more by destructive interference, so that the effect of obliquity alone could be ignored.Cf. Fresnel, 1866–70, vol. 1, pp. 174–5; Buchwald, 1989, pp. 157–8.
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The tilt or obliquity of Mars changes far more than the Earth; hence times of higher humidity are probable.
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The planet could remain at an obliquity of 60° to 90° for periods as long as 10 million years.
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Earth's obliquity oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle. Based on a continuously updated formula, Earth's mean obliquity is currently and decreasing. Over the course of an orbital period, the obliquity usually does not change considerably, and the orientation of the axis remains the same relative to the background of stars. This causes one pole to be directed more toward the Sun on one side of the orbit, and the other pole on the other side—the cause of the seasons on Earth.
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Earth's obliquity may have been reasonably accurately measured as early as 1100 BC in India and China. The ancient Greeks had good measurements of the obliquity since about 350 BC, when Pytheas of Marseilles measured the shadow of a gnomon at the summer solstice. About 830 AD, the Caliph Al-Mamun of Baghdad directed his astronomers to measure the obliquity, and the result was used in the Arab world for many years. In 1437, Ulugh Beg determined the Earth's axial tilt as 23°30′17″ (23.5047°).
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The outer lip is thickened. The sinus is very obscure. The columellar margin is inclined to obliquity. The siphonal canal is extremely short.
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The first of which suggests that at times of higher obliquity the temperature gradient between the poles and the equator in the southern hemisphere is greater during boreal summer (summer in the northern hemisphere). As a result of this gradient the strength of the North African Monsoon increases. A second theory that may explain the existence of an obliquity signature in the North African climate record suggests that obliquity maybe related to changes in the latitude of the tropics. The latitudinal extent of the tropics is roughly defined by the maximum wandering path of the thermal equator.
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Annual almanacs are published listing the derived values and methods of use. Until 1983, the Astronomical Almanac's angular value of the mean obliquity for any date was calculated based on the work of Newcomb, who analyzed positions of the planets until about 1895: : where is the obliquity and is tropical centuries from B1900.0 to the date in question. From 1984, the Jet Propulsion Laboratory's DE series of computer- generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated: : where hereafter is Julian centuries from J2000.0.
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Scientists using computer models to study extreme axial tilts have concluded that high obliquity could cause extreme climate variations, and while that would probably not render a planet uninhabitable, it could pose difficulty for land-based life in affected areas. Most such planets would nevertheless allow development of both simple and more complex lifeforms. Although the obliquity they studied is more extreme than Earth ever experiences, there are scenarios 1.5 to 4.5 billion years from now, as the Moon's stabilizing effect lessens, where obliquity could leave its current range and the poles could eventually point almost directly at the Sun.
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In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. It differs from orbital inclination. At an obliquity of 0 degrees, the two axes point in the same direction; i.e., the rotational axis is perpendicular to the orbital plane.
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Earth's axial tilt (obliquity) is currently about 23.4°. Earth's orbital plane is known as the ecliptic plane, and Earth's tilt is known to astronomers as the obliquity of the ecliptic, being the angle between the ecliptic and the celestial equator on the celestial sphere. It is denoted by the Greek letter ε. Earth currently has an axial tilt of about 23.44°.
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This is unusual for a short period planet. Many short period planets show high orbital obliquity, which was taken as a sign of the scattering of the planet into this short period orbit. It can also be interpreted as the formation of a planet in an inner disk with an axial tilt. But these previous measurements of orbital obliquity were made for giant planets around mature stars.
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So far, it has not been possible to constrain the obliquity of an extrasolar planet. But the rotational flattening of the planet and the entourage of moons and/or rings, which are traceable with high-precision photometry, e.g. by the space-based Kepler space telescope, could provide access to in the near future. Astrophysicists have applied tidal theories to predict the obliquity of extrasolar planets.
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There are many proposed theories as to why this might occur. One such theory involves tidal dissipation and suggests there is a single mechanism for producing hot Jupiters and this mechanism yields a range of obliquities. Cooler stars with higher tidal dissipation damps the obliquity (explaining why hot Jupiters orbiting cooler stars are well aligned) while hotter stars do not damp the obliquity (explaining the observed misalignment).
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B52 These expressions for the obliquity are intended for high precision over a relatively short time span, perhaps several centuries. , p. 226-227, at Google books J. Laskar computed an expression to order good to /1000 years over 10,000 years. , table 8, at SAO/NASA ADS All of these expressions are for the mean obliquity, that is, without the nutation of the equator included.
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An area that today is located between the Tropic of Capricorn and the Tropic of Cancer. However, as the obliquity changes, the overall wandering path of the thermal equator shifts between 22.2° and 24.5° north and south. This wandering may affect the positioning of the North African Summer Monsoon Front and thus impact the perceived strength of the North African Monsoon. Further confirmation of the impacts of obliquity on the North African Monsoonal have been provided through a global fully coupled atmosphere–ocean–sea ice climate model, which confirmed that precession and obliquity can combine to increase precipitation in North Africa through insolation feedbacks.
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Where the obliquity of the ecliptic is not obtained elsewhere, it can be approximated: : \epsilon = 23.439^\circ - 0.0000004^\circ n for use with the above equations.
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The maximum latitude range of the arctic extends to near-equatorial latitudes of 13°N and 13°S when the obliquity goes down to its minimum of 103°. At that time, the arctic circles cover around 78% of the total surface area. The high obliquity induced in latitude variations in arctic zones extending down to near-equatorial regions indicates that the maximum amount of insolation is received at the poles.
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As on Earth, Mars experiences Milankovitch cycles that cause its axial tilt (obliquity) and orbital eccentricity to vary over long periods of time, which has long-term effects on its climate. The variation of Mars's axial tilt is much larger than for Earth because it lacks the stabilizing influence of a large moon like Earth's moon. Mars has a 124,000-year obliquity cycle compared to 41,000 years for Earth.
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However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere.
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There are five climate zones on Pluto which are defined by the sub-solar latitude, each with specific boundaries. However, the latitude ranges of the climate zones expand and shrink in response to the obliquity range of Pluto from a minimum of 103° to a maximum of 127° over the 2.8 million year oscillation period. That means some of the zones have permanent latitude ranges, whereas other zones change their boundaries based on the variation of the axial tilt on a multi-million-year time scale. Permanent boundaries refer to the latitude zones that experience certain characteristics at all times, regardless of the obliquity variation of the dwarf planet over the obliquity oscillation period.
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It was widely believed, during the Middle Ages, that both precession and Earth's obliquity oscillated around a mean value, with a period of 672 years, an idea known as trepidation of the equinoxes. Perhaps the first to realize this was incorrect (during historic time) was Ibn al-Shatir in the fourteenth century and the first to realize that the obliquity is decreasing at a relatively constant rate was Fracastoro in 1538. The first accurate, modern, western observations of the obliquity were probably those of Tycho Brahe from Denmark, about 1584,Dreyer (1890), p. 123 although observations by several others, including al-Ma'mun, al-Tusi, Purbach, Regiomontanus, and Walther, could have provided similar information.
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Eratosthenes most probably used a solstitial armilla for measuring the obliquity of the ecliptic. Hipparchus probably used an armillary sphere of four rings.Editors of Encyclopædia Britannica. (16 November 2006).
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As the incident wavefront approaches this critical obliquity, the refracted wavefront becomes concentrated against the refracting surface, augmenting the secondary waves that produce the reflection back into the first medium.
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J. N. Winn and M. J. Holman (2005),"Obliquity Tides on Hot Jupiters", The Astrophysical Journal, Volume 628, Issue 2, pp. L159-L162. Earth's Moon is in Cassini state 2.
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Arctic, diurnal, and tropical zones of Pluto; oscillation of the zones in response to the obliquity cycle is displayed by dashed lines The tropics of Pluto are defined as the latitude ranges in which the Sun reaches its overhead point, or zenith, at least once during Pluto's orbital period around the Sun. By this definition, the tropics stretch from the latitude of 60°N to 60°S, due to the current obliquity of 120°. However, when the obliquity reaches its minimum value of 103°, the tropics expand to the maximum latitude ranges from 77°N to 77°S. At this period, the tropics cover most of the surface of the dwarf planet, encompassing around 97% of the total surface area.
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Stellar spectrum study, performed in early 2020, has revealed the TRAPPIST-1 star rotational axis is well aligned with the plane of planetary orbits. The stellar obliquity was found to be degrees.
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Obliquity of the ecliptic is the term used by astronomers for the inclination of Earth's equator with respect to the ecliptic, or of Earth's rotation axis to a perpendicular to the ecliptic. It is about 23.4° and is currently decreasing 0.013 degrees (47 arcseconds) per hundred years because of planetary perturbations. , art. 365–367, p. 694–695, at Google books The angular value of the obliquity is found by observation of the motions of Earth and other planets over many years.
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This is continued across the body as a porcellaneous layer, thinning out and disappearing on the columella, which is cut off in front with a long obliquity, whose edge is rounded, but hardly twisted.
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Therefore, with the small tilt variation over time, the Earth has always been thought to have had a seasonal climate, at least in the high latitudes due to the solar effect of changing Earth obliquity.
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The Moon's stabilizing effect will continue for less than 2 billion years. As the Moon continues to recede from Earth due to tidal acceleration, resonances may occur which will cause large oscillations of the obliquity.
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The Chaotic Obliquity of Mars. Science 259, 1294–1297.Laskar, J., A. Correia, M. Gastineau, F. Joutel, B. Levrard, and P. Robutel. 2004. Long term evolution and chaotic diffusion of the insolation quantities of Mars.
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A rod further north would have a north–south shadow, and as an elevation of 90° would be a zero latitude, the complement of the elevation gives the latitude. The Sun is even higher in the sky due to the tilt. The angle added to the elevation by the tilt is known as the obliquity of the ecliptic and at that time was 23° 44′ 40″. The complement of the elevation less the obliquity is 43° 13′, only 5′ in error from Marseille's latitude, 43° 18′.
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Nature, 268, 44-45. showing that, in addition to the known 40-ka period of obliquity (ka = thousand years) and 21-ka period of climatic precession, there are periods of 400 ka, 125 ka, 95 ka and 100 ka in eccentricity, of 54 ka in obliquity and of 23 ka and 19 ka in climatic precession. Under the leadership of Nicholas Shackleton,Shackleton N.J., Berger A., Peltier W.R., 1990. An alternative astronomical calibration of the lower Pleistocene time scale based on ODP site 677. Phil.
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At some point, perturbation effects will probably cause chaotic variations in the obliquity of the Earth, and the axial tilt may change by angles as high as 90° from the plane of the orbit. This is expected to occur between 1.5 and 4.5 billion years from now. A high obliquity would probably result in dramatic changes in the climate and may destroy the planet's habitability. When the axial tilt of the Earth exceeds 54°, the yearly insolation at the equator is less than that at the poles.
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Many of these channels probably carried water, at least for a time. The climate of Mars may have been such in the past that water ran on its surface. It has been known for some time that Mars undergoes many large changes in its tilt or obliquity because its two small moons lack the gravity to stabilize it, as our moon stabilizes Earth; at times the tilt of Mars has even been greater than 80 degreesTouma J. and J. Wisdom. 1993. The Chaotic Obliquity of Mars.
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"Glossary" in Astronomical Almanac Online. (2018). Washington DC: United States Naval Observatory. s.v. obliquity. This value remains about the same relative to a stationary orbital plane throughout the cycles of axial precession. But the ecliptic (i.e.
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The diurnal climate zone of Pluto is defined as the latitudinal ranges where day and night cycle occur for each rotation throughout the entire orbital year. The high mean obliquity and oscillation cycle make a narrow latitudinal band experience a diurnal circle. Pluto experiences the narrowest band of diurnal zone when the obliquity comes down to minimum of 103°, which occurred around ~0.8 million years ago. This band from 13°N to 13°S, extending equally on both sides of the equator, is called the permanent diurnal zone.
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The beds display a pronounced cyclicity, with the precession, obliquity, and eccentricity orbital components all clearly detectable. This enables the beds to be internally dated with a high degree of accuracy, and astrochronological dates agree very well with radiometric dates.
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A long period of continuous winter, typically lasting more than a century, is experienced by the permanent arctic zones in every Pluto orbital period of 248 years over the 2.8 million year obliquity cycle. Due to the variation in the axial tilting of Pluto, the arctic zones also expand and contract over the oscillation cycle. With the current obliquity of 120°, the arctic zones extend from 30°N to 90°N in the northern hemisphere, whereas it is 30°S to 90°S in the southern hemisphere. These two arctic zones together cover 50 percent of the total surface area of Pluto.
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The polar moment of inertia is traditionally determined by combining measurements of spin quantities (spin precession rate and/or obliquity) with gravity quantities (coefficients of a spherical harmonic representation of the gravity field). These geodetic data usually require an orbiting spacecraft to collect.
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Mars has no moon large enough to stabilize its obliquity, which has varied from 10 to 70 degrees. This would explain recent observations of its surface compared to evidence of different conditions in its past, such as the extent of its polar caps.
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Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for the late Amazonian obliquity-driven climate change. Earth Planet. Sci. Lett. 241. 663-671Head, J., et al. 2006. Modification if the dichotomy boundary on Mars by Amazonian mid-latitude regional glaciation. Geophys.
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These conditions and the large obliquity of the photographs hampered geologic interpretation of surface materials in the map area, as they did in the Kuiper (De Hon and others, 1981), Victoria (McGill and King, 1983), and Shakespeare (Guest and Greeley, 1983) quadrangles to the south.
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Ultraviolet light from the Sun can then break the water apart in a process called photodissociation. The hydrogen from the water molecule then escapes into space. The obliquity (axial tilt) of Mars varies considerably on geologic timescales, and has a strong impact on planetary climate conditions.
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Nägele's obliquity is the presentation of the anterior parietal bone to the birth canal during vaginal delivery with the biparietal diameter being oblique to the brim of the pelvis. The synonym for this presentation is anterior asynclitism. It was first described in 1777 by German Karl Nägele.
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For planets and other rotating celestial bodies, the angle of the equatorial plane relative to the orbital plane — such as the tilt of the Earth's poles toward or away from the Sun — is sometimes also called inclination, but less ambiguous terms are axial tilt or obliquity.
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Explanatory Supplement (1961), sec. 2B From 1984, the Jet Propulsion Laboratory's DE series of computer-generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated: where hereafter is Julian centuries from J2000.0.
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Where the obliquity of the SWIR increases so does its length. This lengthening results in a decrease in mantle upwelling and a ridge geometry characteristic of ultra-slow spreading ridges (<12 mm/yr). The orthogonal supersegment is similar to larger ridge segments of the Mid- Atlantic Ridge.
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The point of the columella is cut off with a very slight obliquity, and has a blunt and very slightly twisted edge. The operculum is small, oval, smooth, with hair-like striae. The apex is terminal The colour is pale brownish yellow. R.B. Watson, Mollusca of H.M.S. ‘Challenger’ Expedition.
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A dynamical model explaining this behavior was proposed by Peter Ditlevsen. as PDF This is in support of the suggestion that the late Pleistocene glacial cycles are not due to the weak 100,000-year eccentricity cycle, but a non-linear response to mainly the 41,000-year obliquity cycle.
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Because nutation causes a change to the frame of reference, rather than a change in position of an observed object itself, it applies equally to all objects. Its magnitude at any point in time is usually expressed in terms of ecliptic coordinates, as nutation in longitude (\Delta\psi) and nutation in obliquity (\Delta\epsilon). The largest term in nutation is expressed numerically (in arcseconds) as follows: :\Delta\psi = -17.2\sin\Omega :\Delta\epsilon = 9.2\cos\Omega where \Omega is the ecliptic longitude of the ascending node of the Moon's orbit. By way of reference, the sum of the absolute value of all the remaining terms is 1.4 arcseconds for longitude and 0.9 arcseconds for obliquity.
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Periodic motions of the Moon and of Earth in its orbit cause much smaller (9.2 arcseconds) short-period (about 18.6 years) oscillations of the rotation axis of Earth, known as nutation, which add a periodic component to Earth's obliquity.Explanatory Supplement (1961), sec. 2C The true or instantaneous obliquity includes this nutation.
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An additional suggested cause for the Middle Miocene disruption has been attributed to a shift from a solar insolation cycle that is obliquity dominated to one that is dominated by eccentricity (see Milankovitch cycles). This change would have been significant enough for conditions near the Antarctic continent to allow for glaciation.
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Transactions of the Royal Society of Edinburgh: Earth Sciences, vol. 81 part 4, pp. 251-261. he contributed to improve the age of the Brunhes-Matuyama reversal. He identified the instability of the astronomical periods and the existence of a 1.3-Ma period (Ma = million years) in the amplitude modulation of obliquity.
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Ice ages are driven by changes in Mars's orbit and tilt —also known as obliquity. Orbital calculations show that Mars wobbles on its axis far more than Earth does. The Earth is stabilized by its proportionally large moon, so it only wobbles a few degrees. Mars may change its tilt by many tens of degrees.
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Her work includes analyzing a number of factors, including the distance and type of star a planet orbits, the eccentricity and obliquity of that orbit, the atmosphere of the planet, and the rate of rotation. By exploring the parameter space of what can affect a planet's climate, scientists can narrow the candidates for sustaining life.
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They are parted by shallow rounded furrows of double their breadth. On the first regular whorl they appear as simple beads 9 in number. On the next whorl they assume the form of straight riblets, whose obliquity increases on each successive whorl. The lines of growth, which are quite independent of the riblets, are very slight.
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Others have noted that Glück's poems can be viewed as autobiographical, while her technique of inhabiting various personas, ranging from ancient Greek gods to garden flowers, renders her poems more than mere confessions. As the scholar Helen Vendler has noted: "In their obliquity and reserve, [Glück's poems] offer an alternative to first-person 'confession', while remaining indisputably personal".
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JPL's fundamental ephemerides have been continually updated. For instance, the Astronomical Almanac for 2010 specifies:Astronomical Almanac 2010, p. B52 : These expressions for the obliquity are intended for high precision over a relatively short time span, perhaps several centuries. J. Laskar computed an expression to order good to 0.02″ over 1000 years and several arcseconds over 10,000 years.
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Richard Ellmann, in his review of Station Island for The New York Review of Books, praised the collection writing, "Many of these poems have a tough rind as though the author knew that for his purposes deferred comprehension was better than instant. Obliquity suits him. Heaney's talent, a prodigious one, is exfoliating and augmenting here."Ellmann, Richard.
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The planet might be an inflated planet with an upper mass limit of 20 . DS Tuc Ab will be observed by ESA's CHEOPS mission to characterize the planet. The planet DS Tucanae Ab has a low orbital obliquity (λ = ° or λ = 12 ± 13 °). This means that the orbital plane of this planet aligns with the stellar equator of the star.
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Because the obliquity of the ecliptic is slowly decreasing, the values during the lives of Jaghmini and al-Tusi's differ from modern values. As of 2000, the appropriate solar positions are 6°40′ Gemini and 23°20′ Cancer. Other than specifying the sun's position, the passage by al-Tusi describes how to convert the noontime in Mecca to the local time.
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Many features on Mars, including ones in Protonilus Mensae, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degreesTouma J. and J. Wisdom. 1993. The Chaotic Obliquity of Mars.
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The stellar obliquity , i.e. the axial tilt of a star with respect to the orbital plane of one of its planets, has been determined for only a few systems. But for 49 stars as of today, the sky-projected spin- orbit misalignment has been observed, which serves as a lower limit to . Most of these measurements rely on the Rossiter–McLaughlin effect.
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The Sun moved at an oblique angle to the circles, which obliquity brought it now to the north, now to the south. The circle of the Sun was the ecliptic. It was the center of a band called the zodiac on which various constellations were located. The shadow cast by a vertical rod at noon was the basis for defining zonation.
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Cf. A Treatise on Efficacy, 2004; Conférence sur l'efficacité, 2005. The world of psychology and analysis has begun to adopt the concept of "silent transformation" (cf. The Silent Transformations, 2011); the distinction between the word and speech (cf. Si parler va sans dire, 2006); and the concepts of the allusive (l'allusif), availability (la disponibilité), indirectness (le biais), and obliquity (l'obliquité) (cf.
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In addition, the rotational tilt of the Earth (its obliquity) changes slightly. A greater tilt makes the seasons more extreme. Finally, the direction in the fixed stars pointed to by the Earth's axis changes (axial precession), while the Earth's elliptical orbit around the Sun rotates (apsidal precession). The combined effect is that proximity to the Sun occurs during different astronomical seasons.
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These include solar gravitational effects, the obliquity (tilt) of the Earth's Equator and rotational axis, the inclination of the plane of the lunar orbit and the elliptical shape of the Earth's orbit of the Sun. A compound tide (or overtide) results from the shallow-water interaction of its two parent waves.Le Provost, Christian (1991). Generation of Overtides and compound tides (review).
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Many features on Mars, including many in Casius quadrangle, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degreesTouma J. and J. Wisdom. 1993. The Chaotic Obliquity of Mars.
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These changes in global temperature match with changes in orbital parameters of the Earth's orbit around the Sun. These are called Milankovitch cycles, and these are related to eccentricity, obliquity (axial tilt), and precession of Earth around its axis. These correspond to cycles with periods of 100 kyr, 40 kyr, and 20 kyr. δ18O can also be used to investigate smaller scale climate phenomena.
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In 850, al-Farghani wrote Kitab fi Jawani ("A compendium of the science of stars"). The book primarily gave a summary of Ptolemic cosmography. However, it also corrected Ptolemy's Almagest based on findings of earlier Iranian astronomers. Al- Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the sun and the moon, and the circumference of the earth.
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In 850, al- Farghani wrote Kitab fi Jawami (meaning "A compendium of the science of stars"). The book primarily gave a summary of Ptolemic cosmography. However, it also corrected Ptolemy based on findings of earlier Arab astronomers. Al- Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun and the Moon, and the circumference of the Earth.
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Perhaps one of the most apparent factors contributing to Earth climate change is the angle at which the earth is tilted. This is the angle at which Earth's axis of rotation is from the vertical, also known as Earth's obliquity. Earth's current tilt angle is approximately 23.5 degrees. The axial tilt angle affects climate largely by determining which parts of the earth get more sunlight during different stages of the year.
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The Natural History Of Stafford-shire, pages 2–3, Robert Plot LL.D., Oxford The Theatre, 1686. The phenomenon would have been visible well before the seventeenth century. However, the alignment of sun and landscape is subject to change over the centuries as it is affected by the Earth's axial precession. This was realised by Plot who suggested that the sunset could be used to measure the obliquity of the ecliptic.
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The upper portion is now set at an angle equal to the obliquity of the ecliptic, which allows the instrument to give ecliptic coordinates. This measures the celestial bodies now on celestial latitude and longitude scales which allow for greater precision and accuracy in making measurements. These three differing configurations allowed for added convenience in taking readings and made once tedious and complicated measuring more streamlined and simple.
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The tilt or obliquity of the axis of the planet changes a great deal. The Earth’s tilt changes little because our rather large moon stabilizes the Earth. Mars only has two very small moons that do not possess enough gravity to stabilize its tilt. When the tilt of Mars exceeds around 40 degrees (from today's 25 degrees), ice is deposited in certain bands where much mantle exists today.
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He also wrote that, although the Sun and Moon were in conjunction and opposition with each other once a month, this did not mean the Sun would be eclipsed every time their paths met, because of the small obliquity of their orbital paths.Dong (2000), 71–72. The original diagram of Su Song's book of 1092 showing the inner workings of his clocktower; a mechanically rotated armillary sphere crowns the top.
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The event lasted around 200,000 years, spanning the base of the Wenlock epoch. It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle. The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka. The final two data are much further spaced, so harder to link with Milankovic changes.
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The event lasted around 200,000 years, spanning the base of the Wenlock epoch. It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle. The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka. The final two data are much further spaced, so harder to link with Milankovic changes.
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The event lasted around 200,000 years, spanning the base of the Wenlock epoch. It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle. The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka. The final two data are much further spaced, so harder to link with Milankovic changes.
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This obliquity causes Earth's seasons. The Moon's declination also changes, completing a cycle once every lunar nodal period: 27.212 days. Thus, lunar declination ranges from a positive value to a negative one in just under two weeks, and back. Consequently in under a month, the Moon's altitude at upper culmination (when it contacts the observer's meridian) can shift from higher in the sky to lower above the horizon, and back.
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4 October 2017. This is not thought to be adequate to power convection in Triton's icy crust. However, the strong obliquity tides are believed to generate enough additional heat to accomplish this and produce the observed signs of recent surface geological activity. The black material ejected is suspected to contain organic compounds, and if liquid water is present in Triton, it has been speculated that this could make it habitable for some form of life.
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Islam requires its followers to pray five times a day, at specific position of the Sun in the sky. As such, accurate observations of the Sun and its trajectory on the sky were needed. In the late 10th century, Iranian astronomer Abu-Mahmud Khojandi built a massive observatory near Tehran. There, he took accurate measurements of a series of meridian transits of the Sun, which he later used to calculate the obliquity of the ecliptic.
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Gondwana formed part of Pangaea for 150 Ma Gondwana and Laurasia formed the Pangaea supercontinent during the Carboniferous. Pangaea began to break up in the Mid-Jurassic when the Central Atlantic opened. In the western end of Pangaea, the collision between Gondwana and Laurasia closed the Rheic and Palaeo-Tethys oceans. The obliquity of this closure resulted in the docking of some northern terranes in the Marathon, Ouachita, Alleghanian, and Variscan orogenies, respectively.
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If it has any thermal inertia, it is expected to warm for a while after it passes perihelion. "This warming trend on Pluto could easily last for another 13 years," says David J. Tholen. It has also been suggested that a darkening of surface ice may also be the cause, but additional data and modeling is needed. Frost distribution on the surface of Pluto is significantly affected by the dwarf planet's high obliquity.
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Stukeley noticed that the Heel Stone was not precisely aligned on the sunrise. The drifting of the position of the sunrise due to the change in the obliquity of the ecliptic since the monument's erection does not account for this imprecision. Recently, evidence has been found for a neighbour to the Heel Stone, no longer extant. The second stone may have instead been one side of a ‘solar corridor’ used to frame the sunrise.
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It is about 100 km wide and up to 2 km deep—that's deeper than Earth's Grand Canyon. When the tilt or obliquity changes the size of the polar caps change. When the tilt is at its highest, the poles receive far more sunlight and for more hours each day. The extra sunlight causes the ice to melt, so much so that it could cover parts of the surface in 10 m of ice.
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In contrast, when the obliquity rises to its maximum of 127°, the tropics contract down to the minimum latitude range from 53°N to 53°S. At that time, the tropics only cover 80% of the surface area of the planet. Accordingly, the 53°N to 53°S latitude range is called the permanent tropics of Pluto. Since the permanent tropics cover at least 80% of the surface area, most of Pluto's surface always lies in the tropical region.
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The maximum extent of the tropical arctic zone spans between 13° and 77° latitude in both the southern and northern hemispheres (and covers about 75% of the total surface area). With the current obliquity of 120°, the present day's tropical arctic extends from 30°N to 30°S encompassing 50% of Pluto's surface area. The tropical arctic zone is the area that experiences maximum cyclical extremes and is optimum for long-term seasonal layering (e.g. al-Idrisi Montes).
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In earlier times he may have been an inhabitant of the > plains—at any rate no one can place the pitchers of N. Northiana, N. > Veitchii, and N. sanguinea side by side without being struck by their > affinity. Again, a glance at your engraving of N. Northiana reminds one of a > long-urned form of N. Rajah in obliquity of mouth and its wavy-margined > frill. The cauline pitchers of N. Rajah have never yet been figured.
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Obliquity: Why our goals are best achieved indirectly is a book by economist John Kay. It was inspired by an observation of the successful pharmaceutical researcher, Sir James Black: The theme of the book is that businesses and other enterprises are best run by enthusiasts who pursue excellence in their speciality. Financial success then follows from this. But, if financial goals are instead made the primary objective, the business will then lose its vigour and may fail.
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This is the primary cause for the different seasons Earth experiences throughout the year, as well as the intensity of the seasons for higher latitudes. For example, in the Northern Hemisphere, if there were no axial tilt, i.e. Earth's obliquity would be zero degrees, then there would be no change in the seasons from year to year. This would be because there would be no difference in the amount of solar irradiation received, year-round, anywhere on Earth.
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The body whorl occupies more than half the total length of the shell. It is elongated, more convex, slightly rounded at the top, becoming angular towards the middle of the columellar side. It is strongly depressed below this angulation which is accentuated on the dorsal part, and ends in an elongated rectilinear base, surrounded by oblique, entirely white, pressed and granular cords. The aperture is elongated, narrow, rendered sinuous by the obliquity of the siphonal canal and the sinus.
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Those fibers which arise from the ramus of the pubis are short, horizontal in direction, and are inserted into the rough line of the femur leading from the greater trochanter to the linea aspera, medial to the gluteus maximus. Those fibers from the ramus of the ischium are directed downward and laterally with different degrees of obliquity, to be inserted, by means of a broad aponeurosis, into the linea aspera and the upper part of its medial prolongation below.
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Before the Quaternary, northern North America and northern Eurasia are believed to have been covered by thick layers of regoliths, which have been worn away over large areas by subsequent glaciations. Later glaciations were increasingly based on core areas, with thick ice sheets strongly coupled to bare bedrock. However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere.
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Although the Sun appears to rotate uniformly about the Earth, in reality this motion is not perfectly uniform. This is due to the eccentricity of the Earth's orbit (the fact that the Earth's orbit about the Sun is not perfectly circular, but slightly elliptical) and the tilt (obliquity) of the Earth's rotational axis relative to the plane of its orbit. Therefore, sundial time varies from standard clock time. On four days of the year, the correction is effectively zero.
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Remains of Ulugh Beg's mural sextant, Samarkand, Uzbekistan, 15th century. The first known mural sextant was constructed in Ray, Iran, by Abu-Mahmud al-Khujandi in 994. To measure the obliquity of the ecliptic, al-Khujandī invented a device that he called al- Fakhri sextant (al-suds al Fakhrī), a reference to his patron, Buwayhid ruler, Fakhr al Dawla (976–997). This instrument was a sixty-degree arc on a wall aligned along a meridian arc (north-south line).
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In 25,772 years, the points are once again at the same point in the sky where observations began. In addition the tilt, or obliquity, of the Earth's axis is not constant but changes in a cycle of its own. During a cycle that averages about 40,000 years, the tilt of the axis varies between 22.1 and 24.5 degrees. The precession of the axis of a spinning body as seen on a small scale in a gyroscope.
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No images provide a vertical view; in fact, the smallest angle between the planetary surface normal and the camera axis is about 50°. The high obliquity of the images, the wide range in sun-elevation angles, and the complete transection of the quadrangle by the gap in coverage greatly hamper geologic mapping. Only in about 15 percent of the quadrangle, near the southeast corner, do data permit separation of units with the confidence possible in other quadrangles on Mercury.
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Its tilt, also called obliquity, varies greatly because its two tiny moons cannot stabilize it, like our relatively large moon does the Earth. Many features on Mars, including Deuteronilus Mensae, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degreesTouma J. and J. Wisdom. 1993.
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Reudemannoceras is described (Flower and Teichert 1957) as having a somewhat compressed endogastric shell, such that the width is greater than the height, with the venter slightly flattened. Sutures are closely spaced and slope forward from venter to dorsum with the obliquity increasing as growth progressed. The early part of the shell is essentially straight, but afterward expands and is notably curved. The early segments in the siphuncle (Techert 1964) are bulb shaped and the septal necks are short.
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69 in 1744. From 1745 to 1791, Le Monnier visited Saint-Suplice at each summer solstice and, focusing the light with a lens fixed to the opening in the stained-glass window so as to produce a sharp image of the sun on the floor, noted the exact position of the image at noon. From these observations, he calculated a variation of the obliquity of 45" per century (the exact figure is 46".85 per century).
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The outer lip has a slight obliquity, relatively to the axis of the shell. It is slightly crenulated upon the lip, and furnished interiorly with fifteen or sixteen transverse striae which are continued even to the depth of the cavity. The emargination is very oblique, accompanied externally by a thick, rounded, and twisted varix, which, revolving around the axis, terminates below the folds of the columella. This is slightly arcuated; one or two oblique folds are delineated at its base.
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There are various solar/celestial effects that exist which have an effect on Earth's climate. These effects usually occur in cycles, and primarily include how Earth's obliquity, the eccentricity of Earth's orbit, and the precession of the equinoxes and solstices affect Earth's climate. In addition to these effects, there are also other factors that have an effect on Earth's climate. These other factors include how sun activity affects climateSolar cycle#Terrestrial climate and how celestial phenomena, such as meteors, affect Earth's climate.
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Recent results have placed the age at around 4 billion years. The chance that it is tidally locked is approximately 50%. Since it is closer to its star than Earth is to the Sun, it will probably rotate much more slowly than Earth; its day could be weeks or months long (see Tidal effects on rotation rate, axial tilt and orbit). Kepler-186f's axial tilt (obliquity) is likely very small, in which case it would not have tilt- induced seasons like Earth's.
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The humeroulnar joint (ulnohumeral or trochlear joint), is part of the elbow- joint. It is composed of two bones, the humerus and ulna, and is the junction between the trochlear notch of ulna and the trochlea of humerus. It is classified as a simple hinge-joint, which allows for movements of flexion, extension and circumduction. Owing to the obliquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus.
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High correlations of the Dole effect to speleothem δ18O, an indicator for monsoon precipitation, suggest that it is subject to changes in low-latitude terrestrial productivity. Orbital scale variations of the Dole effect, characterized by periods of 20-100 kyr, respond strongly to Earth's orbital eccentricity and precession, but not obliquity. The Dole effect can also be applied as a tracer in sea water, with slight variations in chemistry being used to track a discrete "parcel" of water and determine its age.
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Historically, there have been cyclical ice ages in which glacial sheets periodically covered the higher latitudes of the continents. Ice ages may occur because of changes in ocean circulation and continentality induced by plate tectonics. The Milankovitch theory predicts that glacial periods occur during ice ages because of astronomical factors in combination with climate feedback mechanisms. The primary astronomical drivers are a higher than normal orbital eccentricity, a low axial tilt (or obliquity), and the alignment of summer solstice with the aphelion.
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A study using observations from Hubble could not find a variation in the light curve. According to this study the rotational period must be larger than 10 hours. A study with CSA's NEOSSat found a period of 13.2 ± 0.2 day, which is unlikely the nuclear spin. Monte Carlo simulations based on the available orbit determinations suggest that the equatorial obliquity of 2I/Borisov could be about 59 degrees or 90 degrees, the latter is favored for the latest orbit determination.
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All cases of reflection or refraction by a surface are then explained simply by considering the secondary waves emitted from that surface. In the case of refraction from a medium of slower propagation to a medium of faster propagation, there is a certain obliquity of incidence beyond which it is impossible for the secondary wavefronts to form a common tangent in the second medium;Huygens, 1690, tr. Thompson, pp.39–40. this is what we now call the critical angle.
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However climate models show that ice is not stable at Hecates Tholus today, pointing to climate change since the glaciers were active. It has been shown that the age of the glaciers correspond to a period of increased obliquity of Mars' rotational axis. The volcano is at location 32.12°N 150.24°E, in the volcanic province Elysium, and has a diameter of 182 km. It is the northernmost of the Elysium volcanoes; the others are Elysium Mons and Albor Tholus.
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The neck is flattened from before backward, contracted in the middle, and broader laterally than medially. The vertical diameter of the lateral half is increased by the obliquity of the lower edge, which slopes downward to join the body at the level of the lesser trochanter, so that it measures one-third more than the antero-posterior diameter. The medial half is smaller and of a more circular shape. The anterior surface of the neck is perforated by numerous vascular foramina.
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Rotations of the small moons of Pluto (animation; 01:00; released 10 November 2015) Prior to the New Horizons mission, Nix, Hydra, Styx, and Kerberos were predicted to rotate chaotically or tumble. However, New Horizons imaging found that they had not tidally spun down to near a spin synchronous state where chaotic rotation or tumbling would be expected. New Horizons imaging found that all 4 moons were at high obliquity. Either they were born that way, or they were tipped by a spin precession resonance.
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During elbow extension, however, the oblique posterior part makes contact with the trochlear notch on the ulna so that this obliquity forces the main axis of the forearm to form a small angle with that of the upper arm. This angle is known as the carrying angle and is more prominent in women than in men. Less frequently, the anterior part is oblique too, but in the opposite direction of the posterior side. Consequently, during full elbow flexion, the hand tends to rest outside the shoulder.
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The angle between the Earth's equatorial plane and the ecliptic, ε, is called the obliquity of the ecliptic and ε ≈ 23.4°. An equinox occurs when the earth is at a position in its orbit such that a vector from the earth toward the sun points to where the ecliptic intersects the celestial equator. The equinox which occurs near the first day of spring (with respect to the North hemisphere) is called the vernal equinox. The vernal equinox can be used as a principal direction for ECI frames.
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Variations of cycle times, curves determined from ocean sediments In fact, from 1–3 million years ago, climate cycles did match the 41,000-year cycle in obliquity. After 1 million years ago, the Mid-Pleistocene Transition (MPT) occurred with switch to the 100,000-year cycle matching eccentricity. The transition problem refers to the need to explain what changed 1 million years ago. The MPT can now be reproduced in numerical simulations that include a decreasing trend in carbon dioxide and glacially induced removal of regolith.
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An often-cited 1980 orbital model by Imbrie predicted "the long-term cooling trend that began some 6,000 years ago will continue for the next 23,000 years." More recent work suggests that orbital variations should gradually increase 65° N summer insolation over the next 25,000 years. Earth's orbit will become less eccentric for about the next 100,000 years, so changes in this insolation will be dominated by changes in obliquity, and should not decline enough to permit a new glacial period in the next 50,000 years.
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20 mm/yr and in the SWIR there is an absence of volcanic activity along stretches of ridge axis. Along large sections, the SWIR runs obliquely relative to the spreading direction, typically about 60°. Because obliquity increases ridge length while decreasing mantle upwelling rates, the SWIR is transitional between slow and ultra-slow ridges. The slow- spreading sections of the SWIR have magmatic segments linked by transform faults, while the ultra-slow sections lack such transforms and have magmatic segments linked by amagmatic troughs.
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The obliquity of some airless planetary bodies in our solar system such as Mercury, the Moon and Ceres is very close to zero. Harold Urey first noted that depressions or craters located near the poles of these bodies will cast persistent shadows that can survive for geologic time periods (million-billion years). The absence of an atmosphere prevents mixing by convection, rendering these shadows extremely cold. If molecules of volatiles such as water ice travel into these permanent shadows, they will become trapped for geologic time periods.
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It does not appear that he has secured any more > money than was essential to feed and clothe his native wards, and to re- > establish them in dwellings. This is a work of Christian charity, defensible > on the most elementary grounds of justice. When Mark Twain accuses Dr. Ament > and his fellow missionaries of "looting" he manifests a mental and moral > obliquity which astonishes and pains his New England neighbors and admirers. > The trouble with our genial humorist is that he is beyond his depth.
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Pluto's polar zone comprises those areas where the Sun never reaches the zenith at any time of the orbital period of the dwarf planet over its entire obliquity cycle. This region always experiences arctic climate, never tropical climate, and it consistently experiences the longest duration of arctic winter and summer during each and every orbital rotation of Pluto. The polar zone has a radius of 13° from each pole. The zone spans from 77°N to 90°N and from 77°S to 90°S, encompassing an area total of 3% of the dwarf planet.
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The correlation between the surface compositional distribution of methane (CH4) and nitrogen (N2) and the climate zones is somewhat speculative. CH4 is widely distributed outside the Tombaugh Regio and Cthulhu Regio, possibly at latitudinal bands of the northern boundary of Cthulhu. Conversely, N2 is concentrated in the latitudes above 30°N coinciding with the permanent arctic climate zone which spans from 37°N latitude to the pole. Some areas on Pluto's surface experience both tropical and arctic climate since both of the climate zones oscillate in response to the obliquity cycle.
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This species differs from Fusiturricula fusinella by the obliquity of the ribs and the disparity in size between the peripheral spiral cords, which are quite equal and equally nodulous in F. fusinella. W.H. Dall (1908): Reports on the Dredging Operations off the West Coast of Central America to the Galapagos, to the West Coast of Mexico, and in the Gulf of California, in charge of Alexander Agassiz, carried on by the U. S. Fish Commission Steamer "Albatross," during 1891, Lieut. Commander Z. L. Tanner, U. S. N., Commanding. XXX VII.
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Based on Goldstone and Arecibo radar images taken in 2012–2013, Brozović et al. have estimated that Apophis is an elongated object 450 × 170 metres in size, and that it is bilobed (possibly a contact binary) with a relatively bright surface albedo of . Its rotation axis has an obliquity of −59° against the ecliptic, which means that Apophis is a retrograde rotator. During the 2029 approach, Apophis's brightness will peak at magnitude 3.1, easily visible to the naked eye if one knows where to look, with a maximum angular speed of 42° per hour.
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Ibn Yunus (c. 950–1009) observed more than 10,000 entries for the Sun's position for many years using a large astrolabe with a diameter of nearly 1.4 meters. His observations on eclipses were still used centuries later in Simon Newcomb's investigations on the motion of the Moon, while his other observations inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn. In 1006, Ali ibn Ridwan observed the supernova of 1006, regarded as the brightest stellar event in recorded history, and left the most detailed description of the temporary star.
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Variations in the climate of the Sahara region can, at the simplest level, be attributed to the changes in insolation because of slow shifts in Earth's orbital parameters. The parameters include the precession of the equinoxes, obliquity, and eccentricity as put forth by the Milankovitch theory. The precession of the equinoxes is regarded as the most important orbital parameter in the formation of the "green Sahara" and "desert Sahara" cycle. A January 2019 MIT paper in Science Advances shows a cycle from wet to dry approximately every 20,000 years.
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Obliquity, otherwise known as tilt, refers to the angle that Earth's axis of rotation makes with a line that is perpendicular to Earth's orbital plane. The current tilt of Earth's axis is roughly 23.5°. However, over long periods of time the tilt of Earth's axis of rotation changes because of the uneven distribution of mass across the planet and gravitational interactions with the Sun, Moon, and planets. Due to these interactions the tilt of Earth's axis of rotation varies between 22.2° and 24.5° on a 41,000 year cycle.
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A spherical asteroid with two wedge-shaped projections. Re-radiated light from the "B" fin has the same magnitude as the "A" fin, but is not parallel to the incoming light. This produces a torque on the object. The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or YORP effect for short, changes the rotation state of a small astronomical body – that is, the body's spin rate and the obliquity of its pole(s) – due to the scattering of solar radiation off its surface and the emission of its own thermal radiation.
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He gives historical data on the life and works of Al-Zarqali and the creation of the Tables of Toledo by astronomers in Toledo patronized by Said Al-Andalusi. He further extends Al-Zarqali's theories on the oscillation of the obliquity of the ecliptic, also presents the spherical trigonometrical formulae, gives a longitude of the solar apogee of 85° 49′ and further confirmed the works of Al-Zarqali. His work seems exceptional in Western Islam, as very complete and accurate, and had a great influence on the development of astronomy in the Maghreb.
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This excess heat is mainly the primordial heat from the early phases of Jupiter's formation, but may result in part from the precipitation of helium into the core. The internal heat may be important for the dynamics of the Jovian atmosphere. While Jupiter has a small obliquity of about 3°, and its poles receive much less solar radiation than its equator, the tropospheric temperatures do not change appreciably from the equator to poles. One explanation is that Jupiter's convective interior acts like a thermostat, releasing more heat near the poles than in the equatorial region.
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It has a minute sinistral nucleus, and six and a half whorls. Its radiating sculpture consists of flexuous incremental lines, and fine wrinkles, which are more prominent toward the periphery on the body whorl and on the early whorls reticulate the spiral sculpture. On the body whorl these lines extend backward with moderate obliquity to the periphery, just above which is the fasciole caused by a well-marked but shallow rounded sulcus. On the base they make a deep rounded concave sweep backward, and then ascend toward the base of the columella.
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Michael L. Gorodetsky, Звездные войны с историей (верификация датировки Альмагеста) (Starry wars with history (Verification of the dating of the Almagest)). Dennis Rawlins points out further that Fomenko's statistical analysis got the wrong date for the Almagest because he took as constant Earth's obliquity when it is a variable that changes at a very slow, but known, rate.Dennis Rawlins, "Recovering Hipparchos’ Last Lost Lustrous Star", DIO 4.3 (1994): 119. Like Dambis and Efremov, Rawlins provides evidence that the Almagest star catalog was based on observations made in the 2nd century BCE by Hipparchus.
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The angle of the Earth's axial tilt with respect to the orbital plane (the obliquity of the ecliptic) varies between 22.1° and 24.5°, over a cycle of about 41,000 years. The current tilt is 23.44°, roughly halfway between its extreme values. The tilt last reached its maximum in 8,700 BCE. It is now in the decreasing phase of its cycle, and will reach its minimum around the year 11,800 CE. Increased tilt increases the amplitude of the seasonal cycle in insolation, providing more solar radiation in each hemisphere's summer and less in winter.
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Some portrayals of God are entirely off-screen. For example: The God who gives the stone tablets to Moses in The Ten Commandments is, in the words of Paul Schrader's commentary to the film, "off-screen to the right". Such biblical epics have less trouble with this obliquity than non-biblical works. This because whilst there is no visual representation of God himself in the source text that such movies are based upon, there are visually representable elements that can be used, from burning bushes to clouds and fire, in the manifestations of God.
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When this obliquity is high, its poles get much more direct sunlight and heat; this causes the ice caps to warm and become smaller as ice sublimes. Adding to the variability of the climate, the eccentricity of the orbit of Mars changes twice as much as Earth's eccentricity. As the poles sublime, the ice is redeposited closer to the equator, which receive somewhat less solar insolation at these high obliquities. Computer simulations have shown that a 45° tilt of the Martian axis would result in ice accumulation in areas that display glacial landforms.
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The rotational offset of the tidal bulge exerts a net torque on the Moon, boosting it while slowing the Earth's rotation (not to scale). The tidal acceleration of the Moon slows the rotation rate of the Earth and increases the Earth-Moon distance. Friction effects—between the core and mantle and between the atmosphere and surface—can dissipate the Earth's rotational energy. These combined effects are expected to increase the length of the day by more than 1.5 hours over the next 250 million years, and to increase the obliquity by about a half degree.
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To obtain agreement with experimental results, he had to include additional arbitrary assumptions about the phase and amplitude of the secondary waves, and also an obliquity factor. These assumptions have no obvious physical foundation but led to predictions that agreed with many experimental observations, including the Poisson spot. Poisson was a member of the French Academy, which reviewed Fresnel's work. He used Fresnel's theory to predict that a bright spot ought to appear in the center of the shadow of a small disc, and deduced from this that the theory was incorrect.
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Because the Earth's equator is itself inclined at an angle of about 23.4° to the ecliptic (the obliquity of the ecliptic, \epsilon), these effects combine to vary the inclination of the Moon's orbit to the equator by between 18.4° and 28.6° over the 18.6 year period. This causes the orientation of the Earth's axis to vary over the same period, with the true position of the celestial poles describing a small ellipse around their mean position. The maximum radius of this ellipse is the constant of nutation, approximately 9.2 arcseconds. Smaller effects also contribute to nutation.
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The very precise observations served for the new Shoushi calendar (Season-Granting Calendar) of 1281, which was in use for 364 years. The length of the tropical year was determined to 365 d 5 h 49 m 20 s, a value in accord with the value of the Gregorian Calendar, but obtained 300 years earlier. In 1787, Laplace applied these measurements to check his calculations on the secular changes of the obliquity of the ecliptic and the eccentricity of the Earth's orbit. It is the first in a series of 27 observatories built in the early Yuan dynasty.
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While the value of eccentricity does impact the distance of the Earth from the Sun, its primary impact on insolation comes from its modulating effect on the procession cycle. For example, when the orbit of the Earth is highly elliptical one hemisphere will have hot summers and cold winters, corresponding to a larger than average yearly insolation gradient. At the same time the other hemisphere will have warm summers and cool winters due to a smaller than average yearly insolation gradient. Like obliquity, eccentricity is not considered to be a primary driver of the strength of the North African Monsoon.
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For most planets, the rotation period and axial tilt (also called obliquity) are not known, but a large number of planets have been detected with very short orbits (where tidal effects are greater) that will probably have reached an equilibrium rotation that can be predicted (i.e. tidal lock, spin–orbit resonances, and non-resonant equilibria such as retrograde rotation). Gravitational tides tend to reduce the axial tilt to zero but over a longer timescale than the rotation rate reaches equilibrium. However, the presence of multiple planets in a system can cause axial tilt to be captured in a resonance called a Cassini state.
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Map of earthquake locations, showing depth contours on top of downgoing slab At the Kurile-Kamchatka Trench, the Pacific Plate is subducting beneath the Okhotsk Plate, a microplate formerly considered to be part of the North American Plate. The convergence rate ranges from ≈75 mm/yr in the north to ≈83 mm/yr at the southern end. Obliquity of convergence increases to the south, where the transpressional stress is partitioned into trench-normal thrust earthquakes and trench-parallel strike-slip earthquakes. This partitioning results in westward translation of the Kurile forearc relative to the North American Plate.
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There is a strong resemblance between the Terceira Rift and other ultra- or super- slow spreading ridges, such as the Gakkel Rift and the Southwest Indian ridges. In particular, high obliquity values of 40°-65°, and a magmatic segmentation wavelength of 100 km, are similar to other very slow rifts. Rift valleys present along the rift are 1000–2200 m deep, and 30–60 km wide, similar to the Mid-Atlantic Ridge median valley. However, the amplitude of the Terceira Rift along-strike topography is 2000–4000 m, which is much larger than expected for ultraslow spreading ridges.
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Assisted by a village mathematician named Ambrose Clarke, Pearson began the reobservation and computation of the 520 stars tabulated for occultations in his Practical Astronomy during the same year. He presented the resulting catalogue to the Royal Astronomical Society on 11 June 1841. Pearson observed Halley's comet on 29 October 1835, and in 1839 he deduced a value for the obliquity of the ecliptic from his own research. He died on 6 September 1847 at South Kilworth, and a tablet honoring his memory in the church recognizes the respect earned by his exemplary conduct as a clergyman and magistrate.
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When these are relieved with replacement surgery and normal motion and function are restored, the body feels that the limb is now longer than it was. This feeling usually subsides by 6 months after surgery as the body adjusts to the new hip joint. The cause of this feeling is variable, and usually related to abductor muscle weakness, pelvic obliquity, and minor lengthening of the hip during surgery (<1 cm) to achieve stability and restore the joint to pre- arthritic mechanics. If the limb length difference remains bothersome to the patient more than 6 months after surgery, a shoe lift can be used.
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Of all the orbital cycles, Milankovitch believed that obliquity had the greatest effect on climate, and that it did so by varying the summer insolation in northern high latitudes. Therefore, he deduced a 41,000-year period for ice ages.; see also However, subsequent research has shown that ice age cycles of the Quaternary glaciation over the last million years have been at a period of 100,000 years, which matches the eccentricity cycle. Various explanations for this discrepancy have been proposed, including frequency modulation or various feedbacks (from carbon dioxide, cosmic rays, or from ice sheet dynamics).
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This was confirmed by al-Birūni, al-Marrākushī and al-Kāshī. Al-Khujandī used his device to measure the sun's angle above the horizon at the summer and winter solstices; these two measurements allow computation of the latitude of the sextant's location and the obliquity of the ecliptic. Ulugh Beg constructed a Fakhri Sextant that had a radius of 40.4 meters, the largest instrument of its type in the 15th century. Housed in the Ulugh Beg Observatory, the sextant had a finely constructed arc with a staircase on either side to provide access for the assistants who performed the measurements.
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The westernmost region of the Gulf, where the Tadjoura Ridge is located, has an anomalously high mantle temperature due to its proximity to the Afar plume. The result of this is higher degrees of melting and magmatism below the ridge, which allows for longer spreading segments without transform faults. The difference in segmentation between the Aden and Sheba ridges can be explained by varying degrees of obliquity. The ocean-continent transition (OCT) of the Sheba ridge formed parallel to the syn-rift structure, whereas the OCT of the Aden ridge formed oblique to the syn-rift structure.
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But between these hostile environments, there would be a sliver of habitability, which could support life. Kepler-186e's axial tilt (obliquity) is likely very small, in which case it would not have tilt-induced seasons as Earth and Mars do. Its orbit is probably close to circular, so it will also lack eccentricity-induced seasonal changes like those of Mars. However, the axial tilt could be larger (about 23 degrees) if another undetected nontransiting planet orbits between it and Kepler-186f; planetary formation simulations have shown that the presence of at least one additional planet in this region is likely.
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Because Earth's rotational axis is not perpendicular to its orbital plane, Earth's equatorial plane is not coplanar with the ecliptic plane, but is inclined to it by an angle of about 23.4°, which is known as the obliquity of the ecliptic.Explanatory Supplement (1992), p. 733 If the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes. The Sun, in its apparent motion along the ecliptic, crosses the celestial equator at these points, one from south to north, the other from north to south.
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Because of Earth's axial tilt (often known as the obliquity of the ecliptic), the inclination of the Sun's trajectory in the sky (as seen by an observer on Earth's surface) varies over the course of the year. For an observer at a northern latitude, when the north pole is tilted toward the Sun the day lasts longer and the Sun appears higher in the sky. This results in warmer average temperatures, as additional solar radiation reaches the surface. When the north pole is tilted away from the Sun, the reverse is true and the weather is generally cooler.
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The distance to the Moon will increase by about 1.5 Earth radii during the same period. Based on computer models, the presence of the Moon appears to stabilize the obliquity of the Earth, which may help the planet to avoid dramatic climate changes. This stability is achieved because the Moon increases the precession rate of the Earth's rotation axis, thereby avoiding resonances between the precession of the rotation and precession of the planet's orbital plane (that is, the precession motion of the ecliptic). However, as the semimajor axis of the Moon's orbit continues to increase, this stabilizing effect will diminish.
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Developments in face-hardened armour in the late nineteenth and early to mid-twentieth centuries revealed that such armour was less effective against glancing oblique impacts. The hardened face layer's brittleness was counterproductive against such impacts. Consequently, alongside face hardened armour such as KCA, homogeneous armour types that combined ductility and tensile strength were developed to protect against glancing impacts. Homogeneous armour was typically used for deck armour, which is subject to more high-obliquity impacts and, on some warships such as and battleships, for lower belt armour below the waterline to protect against shells that land short and dive underwater.
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Copernicus' version of trepidation combined the oscillation of the equinoxes (now known to be a spurious motion) with a change in the obliquity of the ecliptic (axial tilt), acknowledged today as an authentic motion of the Earth's axis. Trepidation was a feature of Hindu astronomy and was used to compute ayanamsha for converting sidereal to tropical longitudes. The third chapter of the Suryasiddhanta, verses 9-10, provides the method for computing it, which E. Burgess interprets as 27 degree trepidation in either direction over a full period of 7200 years, at an annual rate of 54 seconds.
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The permanent diurnal zone covers 22 percent of the total areas of the dwarf planet. The region experiences a continuous sunrise and sunset for each and every Pluto rotation period of 6.4 days over a time period of 10 million years. The present-day diurnal climate zone of Pluto spans from 30°N to 30°S, encompassing 50% of the total surface area, due to the current axial tilt of 120°. As obliquity changes to rise from this value, the diurnal zone will expand to the maximum from 37°N to 37°S (covering a total area of 60%), which will be reached in roughly 600,000 years.
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The tropical arctic zone includes the region that overlaps between tropical and arctic zones extending between 13°N to 77°N and 13°S to 77°S. At this latitudinal range the zones cover 75% of the total surface area. However, like the oscillation of tropical (between 53° and 77° latitude) and arctic (between 13° and 37° latitude) zones, the tropical arctic zone also expands and contrasts over the course of the obliquity cycle. Only the latitude range between 37° to 53° in each hemisphere remains stable over the period, and therefore, those bands are called the permanent tropical arctic zones on Pluto (which covers 20% of the total area).
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Given his strong interest in astronomy, Oriani was appointed on the staff of the Observatory of Brera in Milan in 1776, becoming assistant astronomer in 1778 and director in 1802. In 1778 he began publishing various in-depth dissertations on astronomical objects, the Effemeridi di Milano (Ephemerides of Milan). A very capable astronomer, Oriani's work began to attract considerable attention. His research in the areas of astronomic refraction, the obliquity of the ecliptic, and orbital theory were of considerable noteworthiness in themselves; but his greatest achievement was his detailed research of the planet Uranus, which had been discovered by Sir William Herschel in 1781.
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The problem is that in September the Sun takes less time (as measured by an accurate clock) to make an apparent revolution than it does in December; 24 "hours" of solar time can be 21 seconds less or 29 seconds more than 24 hours of clock time. This change is quantified by the equation of time, and is due to the eccentricity of the Earth's orbit (i.e. the Earth's orbit is not perfectly circular, meaning that the EarthSun distance varies throughout the year), and the fact that the Earth's axis is not perpendicular to the plane of its orbit (the so-called obliquity of the ecliptic).
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These factors include the angle of Earth's axial tilt (also known as Earth's obliquity), the eccentricity of Earth's orbit (how circular/elliptical Earth's orbit is), and Earth's position in time in the precession of the solstices and equinoxes (with different Earth-Sun distances during any given season).Ruddiman, William F. "Earth's Climate Past and Future, 2nd Edition." Although these are the primary three factors in shaping Earths climate, there are other, external, factors that can help shape Earth's climate. These external factors usually affect Earth climate on a very different time scale than the other three, and include factors such as meteors striking Earth and geomagnetic storms.
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The precise orientation of the Egyptian pyramids serves as a lasting demonstration of the high degree of technical skill in watching the heavens attained in the 3rd millennium BCE. It has been shown the pyramids were aligned towards the pole star, which, because of the precession of the equinoxes, was at that time Thuban, a faint star in the constellation of Draco.Ruggles, C.L.N. (2005), Ancient Astronomy, pages 354-355. ABC-Clio. . Evaluation of the site of the temple of Amun-Re at Karnak, taking into account the change over time of the obliquity of the ecliptic, has shown that the Great Temple was aligned on the rising of the midwinter Sun.
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The jump to this excess over p will occur in only beginning now because the secular decrease in precession is beginning to cross a resonance in Earth's orbit caused by the other planets. According to Ward, when, in about 1,500 million years, the distance of the Moon, which is continuously increasing from tidal effects, has increased from the current 60.3 to approximately 66.5 Earth radii, resonances from planetary effects will push precession to 49,000 years at first, and then, when the Moon reaches 68 Earth radii in about 2,000 million years, to 69,000 years. This will be associated with wild swings in the obliquity of the ecliptic as well.
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In a note that Buchwald dates in the summer of 1818, Fresnel entertained the idea that unpolarized waves could have vibrations of the same energy and obliquity, with their orientations distributed uniformly about the wave-normal, and that the degree of polarization was the degree of non-uniformity in the distribution. Two pages later he noted, apparently for the first time in writing, that his phase- inversion rule and the non-interference of orthogonally-polarized beams would be easily explained if the vibrations of fully polarized waves were "perpendicular to the normal to the wave"—that is, purely transverse.Buchwald, 1989, pp. 225–6; Fresnel, 1866–70, vol.
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During the warming in the early Eocene between 52 and 55 million years ago, there were a series of short-term changes of carbon isotope composition in the ocean. These isotope changes occurred due to the release of carbon from the ocean into the atmosphere that led to a temperature increase of at the surface of the ocean. These hyperthermals led to increased perturbations in planktonic and benthic foraminifera, with a higher rate of sedimentation as a consequence of the warmer temperatures. Recent analysis of and research into these hyperthermals in the early Eocene has led to hypotheses that the hyperthermals are based on orbital parameters, in particular eccentricity and obliquity.
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Rotation, precession, and nutation in obliquity of a planet Nutation (from Latin nūtātiō, "nodding, swaying") is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behaviour of a mechanism. In an appropriate reference frame it can be defined as a change in the second Euler angle. If it is not caused by forces external to the body, it is called free nutation or Euler nutation. A pure nutation is a movement of a rotational axis such that the first Euler angle is constant.
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The Eemian climate is believed to have been warmer than the current Holocene.Arctic Council, Impacts of a Warming Climate: Arctic Climate Impact Assessment, Cambridge U. Press, Cambridge, 2004 Changes in the Earth's orbital parameters from today (greater obliquity and eccentricity, and perihelion), known as Milankovitch cycles, probably led to greater seasonal temperature variations in the Northern Hemisphere. During summer months, temperatures in the Arctic region were about 2-4 °C higher than today. The warmest peak of the Eemian was around 125,000 years ago, when forests reached as far north as North Cape, Norway (which is now tundra) well above the Arctic Circle at .
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First, not surprisingly, Newton pointed out the relationship between TIR and dispersion: when a beam of white light approaches a glass-to-air interface at increasing obliquity, the most strongly-refracted rays (violet) are the first to be "taken out" by "total Reflexion", followed by the less-refracted rays.Newton, 1730, pp.56–62,264. Second, he observed that total reflection could be frustrated (as we now say) by laying together two prisms, one plane and the other slightly convex; and he explained this simply by noting that the corpuscles would be attracted not only to the first prism, but also to the second.Newton, 1730, pp.371–2.
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STS is a homogeneous Krupp-type steel developed around 1910. The development of such homogeneous steel resulted in testing which showed that face-hardened armor was less effective against high-obliquity glancing impacts. Around 1910, Carnegie Steel developed a new nickel-chrome-vanadium alloy-steel that offers improved protection over the prior nickel steel armor, though vanadium was no longer used after 1914. This alloy-steel became known as "Special Treatment Steel (STS)"; it became the U.S. Navy Bureau of Construction and Repair (later Bureau of Ships) standard form of high-percentage nickel steel used on all portions of a warship needing homogeneous direct impact protection armor.
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In particular, during the last 800,000 years, the dominant period of glacial–interglacial oscillation has been 100,000 years, which corresponds to changes in Earth's orbital eccentricity and orbital inclination. Yet this is by far the weakest of the three frequencies predicted by Milankovitch. During the period 3.0–0.8 million years ago, the dominant pattern of glaciation corresponded to the 41,000-year period of changes in Earth's obliquity (tilt of the axis). The reasons for dominance of one frequency versus another are poorly understood and an active area of current research, but the answer probably relates to some form of resonance in the Earth's climate system.
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However, these moons are all much more distant from their primaries, and are small in comparison; the largest of them (Phoebe) has only 8% of the diameter (and 0.03% of the mass) of Triton. Triton's orbit is associated with two tilts, the obliquity of Neptune's rotation to Neptune's orbit, 30°, and the inclination of Triton's orbit to Neptune's rotation, 157° (an inclination over 90° indicates retrograde motion). Triton's orbit precesses forward relative to Neptune's rotation with a period of about 678 Earth years (4.1 Neptunian years), making its Neptune-orbit-relative inclination vary between 127° and 180°. That inclination is currently 130°; Triton's orbit is now near its maximum departure from coplanarity with Neptune's.
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There are three parameters that affect the size and shape of the analemma—obliquity, eccentricity, and the angle between the apse line and the line of solstices. Viewed from an object with a perfectly circular orbit and no axial tilt, the Sun would always appear at the same point in the sky at the same time of day throughout the year and the analemma would be a dot. For an object with a circular orbit but significant axial tilt, the analemma would be a figure of eight with northern and southern lobes equal in size. For an object with an eccentric orbit but no axial tilt, the analemma would be a straight east–west line along the celestial equator.
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An object with some "windmill" asymmetry can therefore be subjected to minuscule torque forces that will tend to spin it up or down as well as make its axis of rotation precess. The YORP effect is zero for a rotating ellipsoid if there are no irregularities in surface temperature or albedo. In the long term, the object's changing obliquity and rotation rate may wander randomly, chaotically or regularly, depending on several factors. For example, assuming the Sun remains on its equator, asteroid 951 Gaspra, with a radius of 6 km and a semi- major axis of 2.21 AU, would in 240 Ma (240 million years) go from a rotation period of 12 h to 6 h and vice versa.
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Ocean tides are converted to heat by frictional losses in the oceans and their interaction with the solid bottom and with the top ice crust. In late 2008, it was suggested Jupiter may keep Europa's oceans warm by generating large planetary tidal waves on Europa because of its small but non-zero obliquity. This generates so-called Rossby waves that travel quite slowly, at just a few kilometers per day, but can generate significant kinetic energy. For the current axial tilt estimate of 0.1 degree, the resonance from Rossby waves would contain 7.3 J of kinetic energy, which is two thousand times larger than that of the flow excited by the dominant tidal forces.
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Hazlitt 1930, vol. 11, p. 330. Edward Irving, c. 1823, artist unknown Curious visitors to the chapel, along with some uneasy regular members of the congregation,Hazlitt notes that "the more serious part of his congregation indeed complain". Hazlitt 1930, vol. 11, p. 39. would have been faced with a man of "uncommon height, a graceful figure and action, a clear and powerful voice, a striking, if not a fine face, a bold and fiery spirit, and a most portentous obliquity of vision" with, despite this slight defect, "elegance" of "the most admirable symmetry of form and ease of gesture", as well as "sable locks", a "clear iron-grey complexion, and firm- set features".Hazlitt 1930, vol.
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Provided gravitational interaction of a moon with other satellites can be neglected, moons tend to be tidally locked with their planets. In addition to the rotational locking mentioned above, there will also be a process termed 'tilt erosion', which has originally been coined for the tidal erosion of planetary obliquity against a planet's orbit around its host star. The final spin state of a moon then consists of a rotational period equal to its orbital period around the planet and a rotational axis that is perpendicular to the orbital plane. If the moon's mass is not too low compared to the planet, it may in turn stabilize the planet's axial tilt, i.e.
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Abu Jafar Muhammad ibn Hasan Khazini (; 900–971), also called Al-Khazin, was an Iranian Muslim astronomer and mathematician from Khorasan. He worked on both astronomy and number theory. Al-Khazin was one of the scientists brought to the court in Ray, Iran by the ruler of the Buyid dynasty, Adhad ad-Dowleh, who ruled from 949 to 983 AD. In 959/960 Khazini was required by the Vizier of Ray, who was appointed by ad-Dowleh, to measure the obliquity of the ecliptic. One of Al-Khazin's works Zij al-Safa'ih ("Tables of the disks of the astrolabe") was described by his successors as the best work in the field and they make many references to it.
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Back-arc basin spreading is thought to be due to the combined effects of the sea-anchor force and rapid PH-EU convergence . The obliquity of convergence between PA and the IBM arc system change markedly along the IBM arc system. Plate convergence inferred from earthquake slip vectors is nearly strike-slip in the northernmost Marianas, adjacent to and south of the northern terminus of the Mariana Trough, where the arc has been ‘bowed-out’ by back-arc basin opening, resulting in a trench which strikes approximately parallel to the convergence vectors. Convergence is strongly oblique for most of the Mariana Arc system but is more nearly orthogonal for the southernmost Marianas and most of the Izu-Bonin segments.
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Anaximander was the first astronomer to consider the Sun as a huge mass, and consequently, to realize how far from Earth it might be, and the first to present a system where the celestial bodies turned at different distances. Furthermore, according to Diogenes Laertius (II, 2), he built a celestial sphere. This invention undoubtedly made him the first to realize the obliquity of the Zodiac as the Roman philosopher Pliny the Elder reports in Natural History (II, 8). It is a little early to use the term ecliptic, but his knowledge and work on astronomy confirm that he must have observed the inclination of the celestial sphere in relation to the plane of the Earth to explain the seasons.
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Earth's axial tilt (or obliquity) and its relation to the rotation axis and plane of orbit The axial tilt of Earth is approximately 23.439281° with the axis of its orbit plane, always pointing towards the Celestial Poles. Due to Earth's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of the year. This causes the seasonal change in climate, with summer in the Northern Hemisphere occurring when the Tropic of Cancer is facing the Sun, and winter taking place when the Tropic of Capricorn in the Southern Hemisphere faces the Sun. During the summer, the day lasts longer, and the Sun climbs higher in the sky.
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While typically seen as a control on ice growth and seasonality, the orbital parameters were theorized as a possible control on continental temperatures and seasonality. Simulating the Eocene by using an ice free planet, eccentricity, obliquity, and precession were modified in different model runs to determine all the possible different scenarios that could occur and their effects on temperature. One particular case led to warmer winters and cooler summer by up to 30% in the North American continent, and it reduced the seasonal variation of temperature by up to 75%. While orbital parameters did not produce the warming at the poles, the parameters did show a great effect on seasonality and needed to be considered.
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It reaches plus or minus 17″ in longitude and 9.2″ in obliquity. All other terms are much smaller; the next-largest, with a period of 183 days (0.5 year), has amplitudes 1.3″ and 0.6″ respectively. The periods of all terms larger than 0.0001″ (about as accurately as one can measure) lie between 5.5 and 6798 days; for some reason (as with ocean tidal periods) they seem to avoid the range from 34.8 to 91 days, so it is customary to split the nutation into long-period and short- period terms. The long-period terms are calculated and mentioned in the almanacs, while the additional correction due to the short-period terms is usually taken from a table.
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Atlas V, proposed for OCEANUS, shown here launching a lunar probe into space Ice giant sized planets are the most common type of planet according to Kepler data. The little data available on Uranus, an ice giant planet, come from ground-based observations and the single flyby of the Voyager 2 spacecraft, so its exact composition and structure are essentially unknown, as internal heat flux, and cause of its unique magnetic fields and extreme axial tilt or obliquity, making it a compelling target for exploration according to the Planetary Science Decadal Survey. The primary science objectives of OCEANUS are to study Uranus' interior structure, magnetosphere, and the Uranian atmosphere. The required mission budget is estimated at $1.2 billion.
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A system obeying these laws is said to be in a Cassini state, that is: an evolved rotational state where the spin axis, orbit normal, and normal to the Laplace plane are coplanar while the obliquity remains constant. The Laplace plane is defined as the plane about which a planet or satellite orbit precesses with constant inclination. Cassini state 1 is defined as the situation in which both the spin axis and the orbit normal axis are on the same side of the normal to the Laplace plane. Cassini state 2 is defined as the case in which the spin axis and the orbit normal axis are on opposite sides of the normal to the Laplace plane.
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Thus we know that the celestial bodies are spherical. When the director of the astronomical observatory asked Shen Kuo why eclipses occurred only on an occasional basis while in conjunction and opposition once a day, Shen Kuo wrote: > I answered that the ecliptic and the moon's path are like two rings, lying > one over the other, but distant by a small amount. (If this obliquity did > not exist), the sun would be eclipsed whenever the two bodies were in > conjunction, and the moon would be eclipsed whenever they were exactly in > position. But (in fact) though they may occupy the same degree, the two > paths are not (always) near (each other), and so naturally the bodies do not > (intrude) upon one another.
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The long axis of the figure—the line segment joining the northernmost point on the analemma to the southernmost—is bisected by the celestial equator, to which it is approximately perpendicular, and has a "length" of twice the obliquity of the ecliptic, i.e., about 47°. The component along this axis of the Sun's apparent motion is a result of the familiar seasonal variation of the declination of the Sun through the year. The "width" of the figure is due to the equation of time, and its angular extent is the difference between the greatest positive and negative deviations of local solar time from local mean time when this time-difference is related to angle at the rate of 15° per hour, i.e.
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A more controversial archaeoastronomical approach has been used to date structures that are believed to have been oriented on astronomical principles by measuring their orientation and computing the date in the past when a single specified celestial body, whether the Sun or a selected star, rises or sets at the measured azimuth. The astronomer, Norman Lockyer, applied this method to StonehengeNorman Lockyer and F. C. Penrose, "An Attempt to Ascertain the Date of the Original Construction of Stonehenge from Its Orientation", Proceedings of the Royal Society of London, 69. (1901 - 1902): 137-147. by measuring the orientation of the Stonehenge avenue and comparing it to the position of solstitial sunrise, which changes slowly due to the changing obliquity of the ecliptic.
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Age dates placed nearly all the lobate debris aprons features around the ranges between 1.06 Ga (in the south) and 515 Ma (in the north) in age. The motivation of this work is to identify obliquity-driven climatic shifts, which control the accumulation of ice-rich materials at higher latitudes. In 2015, Colman Gallagher (University College Dublin) and Matthew Balme (Open University) reported on a series of features they observed within a lineated valley fill in the southern Phlegra Montes, most notably interpreting a series of sinuous ridges as eskers in the fill's eastern piedmont. Such landforms are abundant on Earth and are typically indicative of warm and wet climatic conditions known to have been absent on Mars in the late Amazonian period.
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If half of a sphere is > covered with (white) powder and looked at from the side, the covered part > will look like a crescent; if looked at from the front, it will appear > round. Thus we know that the celestial bodies are spherical. When he asked Shen Kuo why eclipses occurred only on an occasional basis while in conjunction and opposition once a day, Shen Kuo wrote: > I answered that the ecliptic and the moon's path are like two rings, lying > one over the other, but distant by a small amount. (If this obliquity did > not exist), the sun would be eclipsed whenever the two bodies were in > conjunction, and the moon would be eclipsed whenever they were exactly in > opposition.
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If this had not happened, the Moon would now lie much closer to the ecliptic and eclipses would be much more frequent. The rotational axis of the Moon is not perpendicular to its orbital plane, so the lunar equator is not in the plane of its orbit, but is inclined to it by a constant value of 6.688° (this is the obliquity). As was discovered by Jacques Cassini in 1722, the rotational axis of the Moon precesses with the same rate as its orbital plane, but is 180° out of phase (see Cassini's Laws). Therefore, the angle between the ecliptic and the lunar equator is always 1.543°, even though the rotational axis of the Moon is not fixed with respect to the stars.
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The morphology of the CIR is characteristic of slow to intermediate ridges. The axial valley is 500–1000 m deep; 50–100 km-long ridge segments are separated by 30 km-long transform faults and 10 km-long non-transform discontinuities. Melt supply comes from axial volcanic ridges that are 15 km- long, 1–2 km wide, and reaches 100–200 m above the axial floor. With a spreading rate of 30 mm/yr near the Equator and 49 mm/yr near the Rodrigues Triple Junction (RTJ) at its southern end, the CIR is an intermediately fast spreading ridge characterised by moderate obliquity and few large offsets, the obvious exception being the almost 300 km-long Marie Celeste Fracture Zone at 18°S.
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When well-regulated mechanical clocks became widespread in the early 19th century, each city began to use local mean solar time. Apparent and mean solar time can differ by up to around 15 minutes (as described by the equation of time) because of the elliptical shape of the Earth's orbit around the Sun (eccentricity) and the tilt of the Earth's axis (obliquity). Mean solar time has days of equal length, and the accumulated difference between the two sums to zero after a year. Greenwich Mean Time (GMT) was established in 1675, when the Royal Observatory was built, as an aid to mariners to determine longitude at sea, providing a standard reference time while each city in England kept a different local time.
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Senemut's tomb, 18th dynastyFull version at Met Museum The precise orientation of the Egyptian pyramids affords a lasting demonstration of the high degree of technical skill in watching the heavens attained in the 3rd millennium BC. It has been shown the Pyramids were aligned towards the pole star, which, because of the precession of the equinoxes, was at that time Thuban, a faint star in the constellation of Draco.Ruggles, C.L.N. (2005), Ancient Astronomy, pages 354–355. ABC-Clio. . Evaluation of the site of the temple of Amun-Re at Karnak, taking into account the change over time of the obliquity of the ecliptic, has shown that the Great Temple was aligned on the rising of the midwinter Sun.Krupp, E.C. (1988).
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Oberon is thought to have formed from an accretion disc or subnebula: a disc of gas and dust that either existed around Uranus for some time after its formation or was created by the giant impact that most likely gave Uranus its large obliquity. The precise composition of the subnebula is not known; however, the relatively high density of Oberon and other Uranian moons compared to the moons of Saturn indicates that it may have been relatively water-poor. Significant amounts of carbon and nitrogen may have been present in the form of carbon monoxide and N2 instead of methane and ammonia. The moons that formed in such a subnebula would contain less water ice (with CO and N2 trapped as clathrate) and more rock, explaining the higher density.
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These latitudes receive less annual insolation than Pluto's polar regions due to its high obliquity (122.5°). The coldest regions on Pluto, on average, are at 30° N. and S. latitude; early in Pluto's history, ice would tend to accumulate at these latitudes in a runaway process due to the positive feedback association of increased albedo, cooling and further ice deposition (similar to the ice segregation that occurred on Iapetus). Simulations suggest that over a period of about a million years, the runaway process would collect much of the ice into a single cap even in the absence of a preexisting basin. The accumulation of dense nitrogen ice would have contributed to making Sputnik Planitia a positive gravity anomaly, but by itself would not have been sufficient to overcome the topographic depression associated with the basin.
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The precession rate is not a constant, but is (at the moment) slowly increasing over time, as indicated by the linear (and higher order) terms in T. In any case it must be stressed that this formula is only valid over a limited time period. It is a polynomial expression centred on the J2000 datum, empirically fitted to observational data, not on a deterministic model of the solar system. It is clear that if T gets large enough (far in the future or far in the past), the T² term will dominate and p will go to very large values. In reality, more elaborate calculations on the numerical model of the Solar System show that the precessional constants have a period of about 41,000 years, the same as the obliquity of the ecliptic.
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The declination of the Sun, δ☉, is the angle between the rays of the Sun and the plane of the Earth's equator. The Earth's axial tilt (called the obliquity of the ecliptic by astronomers) is the angle between the Earth's axis and a line perpendicular to the Earth's orbit. The Earth's axial tilt changes slowly over thousands of years but its current value of about ε = 23°26' is nearly constant, so the change in solar declination during one year is nearly the same as during the next year. At the solstices, the angle between the rays of the Sun and the plane of the Earth's equator reaches its maximum value of 23°26'. Therefore, δ☉ = +23°26' at the northern summer solstice and δ☉ = −23°26' at the southern summer solstice.
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Titania is thought to have formed from an accretion disc or subnebula; a disc of gas and dust that either existed around Uranus for some time after its formation or was created by the giant impact that most likely gave Uranus its large obliquity. The precise composition of the subnebula is not known; however, the relatively high density of Titania and other Uranian moons compared to the moons of Saturn indicates that it may have been relatively water-poor. Significant amounts of nitrogen and carbon may have been present in the form of carbon monoxide and N2 instead of ammonia and methane. The moons that formed in such a subnebula would contain less water ice (with CO and N2 trapped as a clathrate) and more rock, explaining their higher density.
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Ariel is thought to have formed from an accretion disc or subnebula; a disc of gas and dust that either existed around Uranus for some time after its formation or was created by the giant impact that most likely gave Uranus its large obliquity. The precise composition of the subnebula is not known; however, the higher density of Uranian moons compared to the moons of Saturn indicates that it may have been relatively water-poor. Significant amounts of carbon and nitrogen may have been present in the form of carbon monoxide (CO) and molecular nitrogen (N2), instead of methane and ammonia. The moons that formed in such a subnebula would contain less water ice (with CO and N2 trapped as clathrate) and more rock, explaining the higher density.
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The global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas. During the Pliocene the earth climate system response shifted from a period of high frequency-low amplitude oscillation dominated by the 41,000-year period of Earth's obliquity to one of low-frequency, high-amplitude oscillation dominated by the 100,000-year period of the orbital eccentricity characteristic of the Pleistocene glacial-interglacial cycles. The equatorial pacific ocean sea surface temperature gradient was considerably lower than it is today, mean sea surface temperature in the east were substantially warmer than today but similar in the west, this condition has been described as a permanent El Niño state or El Padre. Several mechanisms have been proposed for this pattern, including increased tropical cyclone activity.
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JPL News reported that Oumuamua "is up to one-quarter mile, , long and highly-elongated-perhaps 10 times as long as it is wide". A 2019 paper finds the best models as either a cigar-shape, 1:8 aspect ratio, or disc-shape, 1:6 aspect ratio, with the disc more likely since its rotation doesn't require a specific orientation to see the range of brightnesses observed. Monte Carlo simulations based on the available orbit determination suggest that the equatorial obliquity of Oumuamua could be about 93 degrees, if it has a very prolate or cigar-like shape, or close to 16 degrees, if it is very oblate or disk-like. Light curve observations suggest the object may be composed of dense metal-rich rock that has been reddened by millions of years of exposure to cosmic rays.
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The Sun is directly overhead at solar noon at the Equator on the equinoxes, at the Tropic of Cancer (latitude N) on the June solstice and at the Tropic of Capricorn ( S) on the December solstice. In the Northern Hemisphere, north of the Tropic of Cancer, the Sun is due south of the observer at solar noon; in the Southern Hemisphere, south of the Tropic of Capricorn, it is due north. The elapsed time from the local solar noon of one day to the next is exactly 24 hours on only four instances in any given year. This occurs when the effects of Earth’s obliquity of ecliptic and its orbital speed around the Sun offset each other. These four days for the current epoch are centered on 11 February, 13 May, 25 July, and 3 November.
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Some researchers have proposed that the knobs of western Tartarus Colles are consistent with concurrent interpretations of knobs in Cerberus Palus (downstream of Athabasca Valles), which would suggest that they formed as the result of interactions between lava and water to form what has been termed by some authors as volcanic rootless constructs (VRC). This class of lava-water interactions includes rootless cones, but have fewer genetic implications in their definition, as are not necessarily phreatomagmatic (resulting from the explosion of steam from the sudden evaporation of fluids on contact with lava). The water source is not required to have been added en masse in the form of some aqueous flood - instead possibly being available in the form of an extremely thin and shallow ground ice reservoir whose presence and extent is controlled by obliquity as an orbital forcer.
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The explorer George Windsor Earl who wrote one of the earliest records of the Oitbi, comparing them favourably with the Jaako, comes from the voyager George Windsor Earl remarked on what he perceived to be a Polynesian component in the makeup of the Oitbi:- > Arched eyebrows, straight silky hair, and complexions fairer than those of > the Australian aborigines generally, were by no means uncommon and many > individuals possessed, in a considerable degree, that obliquity in the > position of the eyes, which is considered as being characteristic of some of > the Polynesian tribes. These appearances were even more developed in the > people from the mountain ranges who occasionally visited us. Upon the whole, > I am very much inclined to suppose that there has been some infusion of the > Polynesian blood among the aborigines of this part of the continent.
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From the Eocene epoch onward, the northward movement of Indian Plate collided with the Eurasian Plate and generated the Himalaya Orogenic belt. The relative motion of the Indian plate against the Eurasian plate (Sunda) has two components (1) 36 mm/year right lateral strike-slip, trending in N10°E direction; (2) 7–9 mm/year east-west convergence. The convergent motion is absorbed by a highly oblique subduction zone between the Indian plate and Burma-micro plate and internal deformation in the centre of Myanmar on the Sagaing Fault. The obliquity of the Indo-Burma convergent plate boundary (Arakan Trench and Andaman Trench) increases further northwards, with a minimum angle of 58° at 20°N latitude to 70° near 22°N latitude, and rapidly increases to 90° near 24°N latitude and over 90° to further North.
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Future high-speed infrared-guided missiles will require new dome materials that are substantially more durable than those in use today, while retaining maximum transparency across the entire operational spectrum or bandwidth. A long-standing compromise exists between optical bandpass and mechanical durability within the current group of single-phase (crystalline or glassy) IR transmitting ceramic materials, forcing missile designers to accept substandard overall system performance. Optical nanocomposites may provide the opportunity to engineer new materials that may overcome these traditional limitations. For example, transparent ceramic armor consisting of a lightweight composite has been formed by utilizing a face plate of transparent alumina Al2O3 (or magnesia MgO) with a back-up plate of transparent plastic. The two plates (bonded together with a transparent adhesive) afford complete ballistic protection against 0.30 AP M2 projectiles at 0° obliquity with a muzzle velocity of per second.
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The results from previous missions, and the Phoenix mission in particular, indicate that the ice-cemented ground in the north polar plains is likely to be the most recently habitable place that is currently known on Mars. The near-surface ice likely provided adequate water activity (aw) during periods of high obliquity 5 million years ago, when Mars had an orbital tilt of 45°, compared to the present value of 25° and ground ice may have melted enough to preserve organic molecules, including organic biosignatures. The two Viking landers conducted in 1976 the first, and so far only, search for current life on Mars. The biology experiments sought to detect living organisms based on the hypothesis that microbial life would be widely present in the soils, as it is on Earth, and that it would respond to nutrients added with liquid water.
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VSOP model • Graphic shows variations in five orbital elements: • Precession index and obliquity control insolation at each latitude: • Ocean sediment and Antarctic ice strata record ancient sea levels and temperatures: • Vertical gray line shows present (2000 CE) Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term is named for Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced the Earth's climatic patterns. Similar astronomical hypotheses had been advanced in the 19th century by Joseph Adhemar, James Croll and others, but verification was difficult because there was no reliably dated evidence, and because it was unclear which periods were important.
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He is one of the pioneers who participated in the renaissance of the astronomical theory of paleoclimate (also known as the Milankovitch theory) in the 1970s, and to its promotion and development in the following decades. He has renewed this theory and improved the accuracy of the long term variations of the astronomical parameters used for the calculation of the incoming solar radiation (insolation) over the last and next millions of years. He became known in 1977 for his paper in Nature and later in the Journal of Atmospheric Physics (1978) delivering all the spectral components of the long term variations of eccentricity, obliquity (axial tilt) and climatic precession. His contributions have played a key role in the time scale calibration and interpretation of the paleoclimate records and in the modelling of the glacial-interglacial cycles.
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It is a minimum at the equinoxes, when the Sun's apparent motion is more sloped and yields more change in declination, leaving less for the component in right ascension, which is the only component that affects the duration of the solar day. A practical illustration of obliquity is that the daily shift of the shadow cast by the Sun in a sundial even on the equator is smaller close to the solstices and greater close to the equinoxes. If this effect operated alone, then days would be up to 24 hours and 20.3 seconds long (measured solar noon to solar noon) near the solstices, and as much as 20.3 seconds shorter than 24 hours near the equinoxes. In the figure on the right, we can see the monthly variation of the apparent slope of the plane of the ecliptic at solar midday as seen from Earth.
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Copernicus developed his heliocentric theory after realizing that the retrograde motion of the planets could be explained much better without epicycles, with the Earth orbiting the sun rather than the other way around. Rheticus believed that the heliocentric universe should be adopted because it could explain the phenomena of the precession of the equinoxes and the change in the obliquity of the ecliptic. If the sun was the center of the deferents of the planets, it allowed the circles in the universe to revolve uniformly and regularly, it united all the spheres into one system, and it was a simpler model with fewer explanations necessary. Wittenberg textbooks emphasized the problems of the Copernican theory and how it related to the calendar, lunar motion, and the rejection of the equant. The Narratio prima also contained ideas that were not found in De revolutionibus or in any of Copernicus’s other writings.
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Some authors have proposed that a combination of mechanisms can satisfactorily explain the origin of the Athabasca Valles system - namely, the large-scale emplacement of low-viscosity lava flows on top of pre-existing glaciers. Apart from ice interactions, this large-scale low-viscosity volcanic efflux is thought to have formed up to a third of the modern Martian surface and has been analogized to Earth's large igneous provinces (LIPs). Individual periods of volcanic activity constituting the modern Elysium Planitia region are thought to have lasted up to 1 Myr, with the rock in the vicinity of the Athabasca Valles being potentially deposited on a timescale of weeks or months. Given the obliquity of Mars during this part of the Amazonian, it has been hypothesized that glaciers were likely actively accumulating in this region of Elysium Planitia at the same time as this period of volcanism.
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By definition, the positions of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle all depend on the tilt of the Earth's axis relative to the plane of its orbit around the sun (the "obliquity of the ecliptic"). If the Earth were "upright" (its axis at right angles to the orbital plane) there would be no Arctic, Antarctic, or Tropical circles: at the poles the sun would always circle along the horizon, and at the equator the sun would always rise due east, pass directly overhead, and set due west. The positions of the Tropical and Polar Circles are not fixed because the axial tilt changes slowly – a complex motion determined by the superimposition of many different cycles (some of which are described below) with short to very long periods. In the year 2000 AD the mean value of the tilt was about 23° 26′ 21″.
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When considering the balance of forces within a regular arch, in which all courses of masonry that make up the barrel are parallel with its abutments and perpendicular to its faces, it is convenient to consider it as a two-dimensional object by taking a vertical section through the body of the arch and parallel with its faces, thereby ignoring any variation in loading along the length of its barrel. In an oblique or skew arch the axis of the barrel is deliberately not perpendicular to the faces, the deviation from perpendicularity being known as the skew angle or the "obliquity" of the arch. For this reason a skew arch needs to be thought of as a three-dimensional object and by considering the direction of the lines of force within the barrel the optimum orientation for the courses of stonework that make the barrel can be decided.
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Ibn Yunus observed more than 10,000 entries for the Sun's position for many years using a large astrolabe with a diameter of nearly 1.4 metres. His observations on eclipses were still used centuries later in Simon Newcomb's investigations on the motion of the Moon, while his other observations of the motions of the planets Jupiter and Saturn inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn.Great Inequalities of Jupiter and Saturn In the 15th century, the Timurid astronomer Ulugh Beg compiled the Zij-i-Sultani, in which he catalogued 1,019 stars. Like the earlier catalogs of Hipparchus and Ptolemy, Ulugh Beg's catalogue is estimated to have been precise to within approximately 20 minutes of arc. In the 16th century, Tycho Brahe used improved instruments, including large mural instruments, to measure star positions more accurately than previously, with a precision of 15–35 arcsec.
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After teaching in secondary schools for a few years, he earned a doctorate from the Sorbonne in 1983.See Riquier, “Mort du philosophe et poète Jean-Louis Chrétien.” Early encounters with the philosopher Henri Maldiney played a significant role in guiding his pursuit of the philosophical vocation.In 2013, Chrétien wrote, "Philosohically, an early encounter with Henri Maldiney introduced me, in an unforgettable way, to the thought of Heidegger..." See Jean-Louis Chrétien, "Attempting to Think Beyond Subjectivity," 228. And see Housset, “Mort du philosophe Jean-Louis Chrétien.” Friendship with the philosopher Vladimir Jankélévitch was another factor, as well as a foundational encounter with the writings of Martin Heidegger.See Riquier, “Mort du philosophe et poète Jean-Louis Chrétien.” He wrote a dissertation under Pierre Aubenque on “The Hermeneutic of Obliquity in Neo-Platonism and Ancient Christianity.”Herméneutique de l'obliquité dans le néoplatonisme et le christianisme antiques.
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Mid-Pliocene reconstructed terrain and ice sheet elevation West Antarctic Ice Sheet extent oscillated at the 40Kyr period of Earth's obliquity, ice sheet collapse occurred when global average temperature were 3 °C warmer than today and carbon dioxide concentration 400 ppmv and resulted in open waters in the Ross Sea. Global sea-level fluctuation associated with ice-sheet collapse were probably of up to 7 meters for west Antarctic and 3 meters for east Antarctic. Model simulations are consistent with reconstructed ice-sheet oscillations and suggest a progression from smaller to larger west Antarctic ice sheet in the last 5 Million years, intervals of ice sheet collapse are much more common in the early-mid Pliocene (5 Ma – 3 Ma), after three-million-year intervals with modern or glacial ice volume became longer and collapse occurs only at times when warmer global temperature coincide with strong austral summer insolation anomalies.
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Hazlitt 1930, vol. 11, p. 44. Hazlitt finds that "the ground work of his compositions is trashy and hackneyed, though set off by extravagant metaphors and an affected phraseology ... without the turn of his head and wave of his hand, his periods have nothing in them ... he himself is the only idea with which he has yet enriched the public mind!" John Kinnaird suggests that in this essay, Hazlitt, with his "penetration" and "characteristically ruthless regard for truth", in his reference to Irving's "portentous obliquity of vision" insinuates that "one eye of Irving's imagination ... looks up to a wrathful God cast in his own image, 'endowed with all his own ... irritable humours in an infinitely exaggerated degree' [while] the other is always squinting askew at the prestigious image of Edward Irving reflected in the gaze of his fashionable audience—and especially in the rapt admiration of the 'female part of his congregation'".
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Armillary Sphere Mu'ayyid al-Din al-'Urdi was an astronomer and engineer who was asked by Tusi to come to Marāgha and help design and construct the observatory. He played a key part in the building of the observatory by producing large water wheels to bring water towards the hill where the observatory would be. Al-'Urdi was noted as one of the instrument makers in the observatory and he wrote the treatise ‘Urḍī's Risāla fī Kayfiyyat al‐arṣād, which is preserved in a manuscript in Paris, and details the instruments in the observatory that were constructed before 1262 AD. Some notable instruments documented in this treatise include the Mural quadrant, an armillary sphere which was used to measure the ecliptic longitude and latitude, a solstitial armilla which was used to determine the obliquity of the ecliptic, and an equinoctial armilla which was used to determine when the sun entered the equatorial plane as well as the path of the sun.
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Frankel, 1976, pp. 149–50; Buchwald, 1989, pp. 99–103; Darrigol, 2012, pp. 195–6. Corpuscular optics was becoming expensive on assumptions. But in 1813, Biot reported that the case of quartz was simpler: the observable phenomenon (now called optical rotation or optical activity or sometimes rotary polarization) was a gradual rotation of the polarization direction with distance, and could be explained by a corresponding rotation (not oscillation) of the corpuscles.Frankel, 1976, pp. 151–2; Darrigol, 2012, p. 196. Early in 1814, reviewing Biot's work on chromatic polarization, Young noted that the periodicity of the color as a function of the plate thickness – including the factor by which the period exceeded that for a reflective thin plate, and even the effect of obliquity of the plate (but not the role of polarization)—could be explained by the wave theory in terms of the different propagation times of the ordinary and extraordinary waves through the plate.Young, 1855, pp. 269–72.
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The winter solstice end of the meridian line The church hosts also a marking in the form of a meridian line inlaid in the paving of the left aisle in 1655; it was calculated and designed by the astronomer Giovanni Domenico Cassini, who was teaching astronomy at the University. A meridian line does not indicate the time: instead, with its length of it is one of the largest astronomical instruments in the world, allowing measurements that were for the time uniquely precise. The sun light, entering through a hole placed at a height in the church wall, projects an elliptical image of the sun, which at local noon falls exactly on the meridian line and every day is different as to position and size. The position of the projected image along the line allows to determine accurately the daily altitude of the sun at noon, from which Cassini was able to calculate with unprecedented precision astronomical parameters such as the obliquity of the ecliptic, the duration of the tropical year and the timing of equinoxes and solstices.
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Rare Earth's assertion that the Moon's stabilization of Earth's obliquity and spin is a requirement for complex life has been questioned. Kasting argues that a moonless Earth would still possess habitats with climates suitable for complex life and questions whether the spin rate of a moonless Earth can be predicted. Although the giant impact theory posits that the impact forming the Moon increased Earth's rotational speed to make a day about 5 hours long, the Moon has slowly "stolen" much of this speed to reduce Earth's solar day since then to about 24 hours and continues to do so: in 100 million years Earth's solar day will be roughly 24 hours 38 minutes (the same as Mars's solar day); in 1 billion years, 30 hours 23 minutes. Larger secondary bodies would exert proportionally larger tidal forces that would in turn decelerate their primaries faster and potentially increase the solar day of a planet in all other respects like Earth to over 120 hours within a few billion years.
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Boxmoor Skew Bridge in 2011, looking in a SSW direction from London Road Boxmoor Skew Bridge detail, showing the chamfered acute quoins and stepped extrados In 1839, George Watson Buck, having also worked on the London and Birmingham Railway under Stephenson before moving to the Manchester and Birmingham Railway, published a work entitled A Practical and Theoretical Essay on Oblique Bridges in which he also acknowledged Nicholson's contribution but, finding it lacking in detail, applied his own original trigonometrical approach and considerable practical experience to the problem. This book was acknowledged as the definitive work on the subject of the helicoidal skew arch and remained a standard text book for railway engineers until the end of the 19th century. Buck's trigonometrical approach allowed every dimension of a skew arch to be calculated without recourse to taking measurements from scale drawings and it allowed him to calculate the theoretical minimum angle of obliquity to which a practical semicircular helicoidal skew bridge could be designed and safely built. Buck, 1839, op. cit.
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Equation of time (red solid line) and its two main components plotted separately, the part due to the obliquity of the ecliptic (mauve dashed line) and the part due to the Sun's varying apparent speed along the ecliptic due to eccentricity of the Earth's orbit (dark blue dash & dot line) The Earth revolves around the Sun. As seen from Earth, the Sun appears to revolve once around the Earth through the background stars in one year. If the Earth orbited the Sun with a constant speed, in a circular orbit in a plane perpendicular to the Earth's axis, then the Sun would culminate every day at exactly the same time, and be a perfect time keeper (except for the very small effect of the slowing rotation of the Earth). But the orbit of the Earth is an ellipse not centered on the Sun, and its speed varies between 30.287 and 29.291 km/s, according to Kepler's laws of planetary motion, and its angular speed also varies, and thus the Sun appears to move faster (relative to the background stars) at perihelion (currently around 3 January) and slower at aphelion a half year later.
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The Mk 19 can launch its grenade at a maximum distance of , though its effective range to a point target is about , since the large rear leaf sight is only graduated as far. The nearest safe distance to launch the grenade is 310 meters in training and 75 meters in combat. Though the Mk 19 has a flash suppressor, it serves only to save the eyesight of its operator, not concealing the weapon's position. For night operation, a picatinny rail quadrant sight can be added for thermal and night vision optics. The Mk 19A is a man-portable crew-served weapon that can fire from a tripod-mounted position or from a vehicle mount, with the latter being the preferred method, as the weapon alone weighs . The primary ammunition for it is the high-explosive dual-purpose M430 grenade. On impact, the grenade can kill anyone within a radius of five meters, and wound them within a radius of 15 meters. It can also punch through of rolled homogeneous armor with a direct hit (0-degree obliquity), which means it can penetrate most infantry fighting vehicles and armored personnel carriers.
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For eras farther out, discrepancies become too large – the exact rate and period of precession may not be computed using these polynomials even for a single whole precession period. The precession of Earth's axis is a very slow effect, but at the level of accuracy at which astronomers work, it does need to be taken into account on a daily basis. Note that although the precession and the tilt of Earth's axis (the obliquity of the ecliptic) are calculated from the same theory and thus, are related to each other, the two movements act independently of each other, moving in opposite directions. Precession exhibits a secular decrease due to tidal dissipation from 59"/a to 45"/a (a = annum = Julian year) during the 500 million year period centered on the present. After short-term fluctuations (tens of thousands of years) are averaged out, the long-term trend can be approximated by the following polynomials for negative and positive time from the present in "/a, where T is in billions of Julian years (Ga): :p = 50.475838 − 26.368583T + 21.890862T2 :p = 50.475838 − 27.000654T + 15.603265T2 Precession will be greater than p by the small amount of +0.135052"/a between and .
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