Modern astronomers focus on the sidereal year, the time it takes Mars to orbit the sun — about 687 days .
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The sidereal year is the length of time it takes for the Earth to return to the same place with respect to the "fix'd" and "constant" stars, so that Orion appears exactly in the same place in the sky, at exactly midnight, 365.2563 days later.
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The "sidereal year" is the length of time it takes for the Earth to return to the same place with respect to the "fix'd" and "constant" stars, so that Orion appears exactly in the same place in the sky, at exactly midnight, 365.2563 days later.
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The Hindu cosmological time cycles explained in the Surya Siddhanta, give the average length of the sidereal year (the length of the Earth's revolution around the Sun) as 365.2563627 days, which is only 1.4 seconds longer than the modern value of 365.256363004 days. This remains the most accurate estimate for the length of the sidereal year anywhere in the world for over a thousand years.
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As these have grown apart, in some countries and cultures the date has been fixed according to the tropical year while in others the astronomical calculation and sidereal year is still used.
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A heliacal year is the interval between the heliacal risings of a star. It differs from the sidereal year for stars away from the ecliptic due mainly to the precession of the equinoxes.
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The Sothic year is the interval between heliacal risings of the star Sirius. It is currently less than the sidereal year and its duration is very close to the Julian year of 365.25 days.
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A Gaussian year is defined as 365.2568983 days. It was adopted by Carl Friedrich Gauss as the length of the sidereal year in his studies of the dynamics of the solar system. A slightly different value is now accepted as the length of the sidereal year, and the value accepted by Gauss is given a special name. A particle of negligible mass, that orbits a body of 1 solar mass in this period, has a mean axis for its orbit of 1 astronomical unit by definition.
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Used for mean new moons, both in Hebrew calendar cycles and in equivalent astronomical cycles. With this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Soon afterwards Simon Newcomb and others discovered that Earth's rotation period varied irregularly, so in 1952, the International Astronomical Union (IAU) defined the second as a fraction of the sidereal year. In 1955, considering the tropical year to be more fundamental than the sidereal year, the IAU redefined the second as the fraction of the 1900.0 mean tropical year.
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Two kinds of year are relevant to understanding his work. The tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). The sidereal year is the length of time that the Sun takes to return to the same position with respect to the stars of the celestial sphere. Precession causes the stars to change their longitude slightly each year, so the sidereal year is longer than the tropical year.
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Using observations of the equinoxes and solstices, Hipparchus found that the length of the tropical year was 365+1/4−1/300 days, or 365.24667 days (Evans 1998, p. 209). Comparing this with the length of the sidereal year, he calculated that the rate of precession was not less than 1° in a century. From this information, it is possible to calculate that his value for the sidereal year was 365+1/4+1/144 days (Toomer 1978, p. 218). By giving a minimum rate he may have been allowing for errors in observation.
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A sidereal year (, ; from Latin "asterism, star") is the time taken by the Earth to orbit the Sun once with respect to the fixed stars. Hence, it is also the time taken for the Sun to return to the same position with respect to the fixed stars after apparently travelling once around the ecliptic. It equals for the J2000.0 epoch. The sidereal year differs from the tropical year, "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees", due to the precession of the equinoxes.
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He reckoned the value as 1° per century, a value that was not improved upon until about 1000 years later, by Islamic astronomers. Since this discovery a distinction has been made between the tropical year and the sidereal year .
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The sidereal year is 20 min 24.5 s longer than the mean tropical year at J2000.0 . Before the discovery of the precession of the equinoxes by Hipparchus in the Hellenistic period, the difference between sidereal and tropical year was unknown. For naked-eye observation, the shift of the constellations relative to the equinoxes only becomes apparent over centuries or "ages", and pre-modern calendars such as Hesiod's Works and Days would give the times of the year for sowing, harvest, and so on by reference to the first visibility of stars, effectively using the sidereal year. The South and Southeast Asian solar New Year, based on Indic influences, is traditionally reckoned by the Sun's entry into Aries and thus the sidereal year, but is also supposed to align with the spring equinox and have relevance to the harvesting and planting season and thus the tropical year.
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The Chinese, Coligny and HebrewThe modern Hebrew calendar, since it is based on rules rather than observations, does not exactly track the tropical year, and in fact the average Hebrew year of ~365.2468 days is intermediate between the tropical year (~365.2422 days) and the sidereal year (~365.2564 days). lunisolar calendars track more or less the tropical year whereas the Buddhist and Hindu lunisolar calendars track the sidereal year. Therefore, the first three give an idea of the seasons whereas the last two give an idea of the position among the constellations of the full moon. The Tibetan calendar was influenced by both the Chinese and Buddhist calendars.
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The Vikram Samvat uses lunar months and solar sidereal years. Because 12 months do not match a sidereal year, correctional months (adhika māsa) are added or (occasionally) subtracted (kshaya masa). A lunar year consists of 12 months, and each month has two fortnights. The lunar days are called tithis.
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Elements by Simon Newcomb The low eccentricity and comparatively small size of its orbit give Venus the least range in distance between perihelion and aphelion of the planets: 1.46 Gm. The planet orbits the Sun once every 225 daysThe sidereal and anomalistic years are both 224.7008 days long. The sidereal year is the time taken to revolve around the Sun relative to a fixed reference frame. More precisely, the sidereal year is one way to express the rate of change of the mean longitude at one instant, with respect to a fixed equinox. The calculation shows how long it would take for the longitude to make one revolution at the given rate.
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Various assertions have been made that other cultures discovered precession independently of Hipparchus. According to Al- Battani, the Chaldean astronomers had distinguished the tropical and sidereal year so that by approximately 330 BC, they would have been in a position to describe precession, if inaccurately, but such claims generally are regarded as unsupported.
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The anomalistic year is the time span between successive closest approaches to the Sun. This may be calculated in the same manner as the sidereal year, but the mean anomaly is used. and travels in doing so,Jean Meeus, Astronomical Algorithms (Richmond, VA: Willmann-Bell, 1998) 238. The formula by Ramanujan is accurate enough.
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The Gaussian year is the sidereal year for a planet of negligible mass (relative to the Sun) and unperturbed by other planets that is governed by the Gaussian gravitational constant. Such a planet would be slightly closer to the Sun than Earth's mean distance. Its length is: : days (365 d 6 h 9 min 56 s).
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As a result of this nodal precession, the time for the Sun to return to the same lunar node, the eclipse year, is about 18.6377 days shorter than a sidereal year. The number of solar orbits (years) during one lunar nodal precession period equals the period of orbit (one year) divided by this difference, minus one: − 1\.
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Throughout the year the star will rise approximately four minutes earlier each successive sunrise. Eventually the star will return to its same relative location at sunrise. This length of time can be called an observational year. Stars that reside close to the ecliptic or the ecliptic meridian will on average exhibit observational years close to the sidereal year of 365.2564 days.
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In the 16th century Copernicus put forward a heliocentric cosmology. Erasmus Reinhold used Copernicus' theory to compute the Prutenic Tables in 1551, and gave a tropical year length of 365 solar days, 5 hours, 55 minutes, 58 seconds (365.24720 days), based on the length of a sidereal year and the presumed rate of precession. This was actually less accurate than the earlier value of the Alfonsine Tables.
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Eccentricity varies primarily due to the gravitational pull of Jupiter and Saturn. However, the semi-major axis of the orbital ellipse remains unchanged; according to perturbation theory, which computes the evolution of the orbit, the semi-major axis is invariant. The orbital period (the length of a sidereal year) is also invariant, because according to Kepler's third law, it is determined by the semi-major axis.
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The medieval astronomical theory of the trepidation of the equinoxes is often attributed to Thābit. But it had already been described by Theon of Alexandria in his comments of the Handy Tables of Ptolemy. According to Copernicus, Thābit determined the length of the sidereal year as 365 days, 6 hours, 9 minutes and 12 seconds (an error of 2 seconds). Copernicus based his claim on the Latin text attributed to Thābit.
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In ancient times, the sun's entry into Aries coincided with the equinox. However, due to the earth's axial precession, the sidereal year is slightly longer than the tropical year, causing the dates to gradually drift apart. Today, the sun's entry into Aries occurs around 18 April, according to astronomical definitions. Some traditional calendars are still marked by the sun's actual movements while others have since been fixed to the Gregorian calendar.
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ABC-Clio instead of using the sidereal year which is used in the Bikrami calendar or the old Nanakshahi and Khalsa calendars. The amended Nanakshahi calendar was adopted in 1998Louis E. Fenech, W. H. McLeod (2014) Historical Dictionary of Sikhism. Rowman & Littlefield but implemented in 2003Knut A. Jacobsen (2008) South Asian Religions on Display: Religious Processions in South Asia and in the Diaspora. Routledge Nesbitt, Eleanor (2016) Sikhism: A Very Short Introduction.
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If the position of the Earth (see above) is reckoned with respect to the fixed stars, then the dates indicate the zodiacal constellation near which the Sun can be found. A calendar of this type is called a sidereal solar calendar . The mean calendar year of such a calendar approximates the sidereal year. Indian calendars like the Hindu calendar, Tamil calendar, Bengali calendar (non-revised) and Malayalam calendar are sidereal solar calendars.
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The ancient Tamil calendar was based on the sidereal year similar to the ancient Hindu solar calendar, except that months were from solar calculations, and originally there was no 60-year cycle as seen in Sanskrit calendar. The year was made up of twelve months and every two months constituted a season. With the popularity of Mazhai vizhavu, traditionally commencement of Tamil year was clubbed on April 14, deviating from the astronomical date of vadavazhi vizhavu.
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Because of this orbit, the asteroid is classified as Aten type, named after the asteroid 2062 Aten. A further characteristic is that its mean orbital period about the Sun is exactly one sidereal year. This means that it is locked into a relationship with the Earth, since such an orbit is only stable under particular conditions. As yet only a few asteroids of this sort are known, locked into a 1:1 resonance with the Earth.
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Earth at seasonal points in its orbit (not to scale) Earth orbit (yellow) compared to a circle (gray) Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi), and one complete orbit takes days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi).Jean Meeus, Astronomical Algorithms 2nd ed, (Richmond, VA: Willmann-Bell, 1998) 238. See Ellipse#Circumference. The formula by Ramanujan is accurate enough.
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Each of these three years can be loosely called an astronomical year. The sidereal year is the time taken for the Earth to complete one revolution of its orbit, as measured against a fixed frame of reference (such as the fixed stars, Latin , singular ). Its average duration is days (365 d 6 h 9 min 9.76 s) (at the epoch J2000.0 = January 1, 2000, 12:00:00 TT).International Earth Rotation and Reference System Service. (2010).
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The orientation (rather than the angle) of Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge. The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion.
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The value of Gauss' constant, exactly as he derived it, had been used since Gauss' time because it was held to be a fundamental constant, as described above. The solar mass, mean solar day and sidereal year with which Gauss defined his constant are all slowly changing in value. If modern values were inserted into the defining equation, a value of would result. It is also possible to set the gravitational constant, the mass of the Sun, and the astronomical unit to 1.
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6 of Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac (Washington, DC: 1898), pp. 10-11. However, the mean tropical year is not suitable as a unit of measurement because it varies from year to year by a small amount, days according to Newcomb. In contrast, the Julian year is defined in terms of SI units so is as accurate as those units and is constant. It approximates both the sidereal year and the tropical year to about ±0.008 days.
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Comparing his measurements with data from his predecessors, Timocharis and Aristillus, he concluded that Spica had moved 2° relative to the autumnal equinox. He also compared the lengths of the tropical year (the time it takes the Sun to return to an equinox) and the sidereal year (the time it takes the Sun to return to a fixed star), and found a slight discrepancy. Hipparchus concluded that the equinoxes were moving ("precessing") through the zodiac, and that the rate of precession was not less than 1° in a century.
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Here Copernicus asserts that the motion of the equinoxes and celestial poles has not been uniform, and argues that consequently they should not be used to define the reference frame with respect to which the motions of the planets are measured, and that the periods of the various planetary motions are more accurately determinable if those motions are measured with respect to the fixed stars. He maintains that he had found the length of the sidereal year to have always been 365 days 6 hours and 10 minutes.
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During the currency of ephemeris time as a standard, the details were revised a little. The unit was redefined in terms of the tropical year at 1900.0 instead of the sidereal year; and the standard second was defined first as 1/31556925.975 of the tropical year at 1900.0,ESAA 1992, p. 79: citing decision of International Committee for Weights and Measures (CIPM), Sept 1954. and then as the slightly modified fraction 1/31556925.9747 instead,ESAA (1992), see page 80, citing CIPM recommendation Oct 1956, adopted 1960 by the General Conference on Weights and Measures (CGPM).
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As most countries and cultures of South and Southeast Asia lie within the Indian cultural sphere, the development of their traditional calendars have been strongly influenced by some form of the Hindu calendar. As in many other calendars, the New Year was based on the northern hemisphere vernal equinox (the beginning of spring). However, the Hindu calendar year was based on the sidereal year (i.e. the movement of the sun relative to the stars), while the Western Gregorian calendar is based on the tropical year (the cycle of seasons).
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Modern discoveries about the true nature of celestial objects have undermined the theoretical basis for assigning meaning to astrological signs, and empirical scientific investigation has shown that predictions and recommendations based on these systems are not accurate. Astrology is generally regarded as pseudoscience. Various approaches to measuring and dividing the sky are currently used by differing systems of astrology, although the tradition of the Zodiac's names and symbols remain consistent. Western astrology measures from Equinox and Solstice points (points relating to equal, longest, and shortest days of the tropical year), while Jyotiṣa or Vedic astrology measures along the equatorial plane (sidereal year).
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The discovery of precession usually is attributed to Hipparchus (190–120 BC) of Rhodes or Nicaea, a Greek astronomer. According to Ptolemy's Almagest, Hipparchus measured the longitude of Spica and other bright stars. Comparing his measurements with data from his predecessors, Timocharis (320–260 BC) and Aristillus (~280 BC), he concluded that Spica had moved 2° relative to the autumnal equinox. He also compared the lengths of the tropical year (the time it takes the Sun to return to an equinox) and the sidereal year (the time it takes the Sun to return to a fixed star), and found a slight discrepancy.
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His value for the length of the sidereal year at 365 days 6 hours 12 minutes 30 seconds is only 3 minutes 20 seconds longer than the modern scientific value of 365 days 6 hours 9 minutes 10 seconds. A close approximation to π is given as: "Add four to one hundred, multiply by eight and then add sixty-two thousand. The result is approximately the circumference of a circle of diameter twenty thousand. By this rule the relation of the circumference to diameter is given." In other words, π ≈ 62832/20000 = 3.1416, correct to four rounded-off decimal places.
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The sidereal year of 365.25636 days is only valid for stars on the ecliptic (the apparent path of the Sun across the sky), whereas Sirius's displacement ~40° below the ecliptic, its proper motion, and the wobbling of the celestial equator cause the period between its heliacal risings to be almost exactly 365.25 days long instead. This steady loss of one relative day every four years over the course of the 365-day calendar meant that the "wandering" day would return to its original place relative to the solar and Sothic year after precisely 1461 civil or 1460 Julian years.
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Grofe believes that this interval is quite close to a whole multiple of the sidereal year, returning the sun to precisely the same position against the background of stars. He proposes that this is an observation of the precession of the equinoxes and that the serpent series shows how the Maya calculated this by observing the sidereal position of total lunar eclipses at fixed points within the tropical year.Grofe, Michael John 2007 The Serpent Series: Precession in the Maya Dresden Codex p. vii Bricker and Bricker think that he based this on misinterpretation of the epigraphy and give their reasons in Astronomy in the Maya Codices.
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The Pale Blue Dot photo taken in 1990 by the Voyager 1 spacecraft showing Earth (center right) from nearly away, about 5.6 hours at light speed. Earth orbits the Sun at an average distance of about every 365.2564 mean solar days, or one sidereal year. This gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, which is one apparent Sun or Moon diameter every 12 hours. Due to this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian.
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A lunisolar calendar is a calendar in many cultures whose date indicates both the Moon phase and the time of the solar year. If the solar year is defined as a tropical year, then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year, then the calendar will predict the constellation near which the full moon may occur. As with all calendars which divide the year into months there is an additional requirement that the year have a whole number of months. In this case ordinary years consist of twelve months but every second or third year is an embolismic year, which adds a thirteenth intercalary, embolismic, or leap month.
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The period for the Sun to return to a node is called the eclipse or draconic year: about 346.6201 d, which is about year shorter than a sidereal year because of the precession of the nodes. If a solar eclipse occurs at one new moon, which must be close to a node, then at the next full moon the Moon is already more than a day past its opposite node, and may or may not miss the Earth's shadow. By the next new moon it is even further ahead of the node, so it is less likely that there will be a solar eclipse somewhere on Earth. By the next month, there will certainly be no event.
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By now (the yellow grid) it has shifted (red arrow) to somewhere in the constellation of Pisces. Note that this is an astronomical description of the precessional movement and the vernal equinox position in a given constellation may not imply the astrological meaning of an Age carrying the same name, as they (ages and constellations) only have an exact alignment in the "first point of Aries", meaning once in each c. 25800 (Great Sidereal Year). The Earth, in addition to its diurnal (daily) rotation upon its axis and annual rotation around the Sun, incurs a precessional motion involving a slow periodic shift of the axis itself: approximately one degree every 72 years.
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Aryabhata asserted that the Moon, planets, and asterisms shine by reflected sunlight,Hayashi (2008), "Aryabhata I", Encyclopædia Britannica.Gola, 5; p. 64 in The Aryabhatiya of Aryabhata: An Ancient Indian Work on Mathematics and Astronomy, translated by Walter Eugene Clark (University of Chicago Press, 1930; reprinted by Kessinger Publishing, 2006). "Half of the spheres of the Earth, the planets, and the asterisms is darkened by their shadows, and half, being turned toward the Sun, is light (being small or large) according to their size." correctly explained the causes of eclipses of the Sun and the Moon, and calculated values for π and the length of the sidereal year that come very close to modern accepted values.
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The mass of this planet is exact since the inclination of the orbit is known, typical for transiting planets. This is a so-called “hot Jupiter” because this Jupiter-like gas giant planet orbits in a really close torch orbit around the star, making this planet extremely hot (in the order of a thousand kelvins). The distance from the star is roughly 20 times smaller than that of Earth from the Sun, which places the planet roughly 8 times closer to its star than Mercury is from the Sun. The “year” on this planet lasts only 3 days, 1 hour, 49 minutes, and 54 seconds, compared with Earth's 365 days, 6 hours, 9 minutes, and 10 seconds in a sidereal year.
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For example, suppose that the Earth's orbital position is marked at the summer solstice, when the Earth's axial tilt is pointing directly toward the Sun. One full orbit later, when the Sun has returned to the same apparent position relative to the background stars, the Earth's axial tilt is not now directly toward the Sun: because of the effects of precession, it is a little way "beyond" this. In other words, the solstice occurred a little earlier in the orbit. Thus, the tropical year, measuring the cycle of seasons (for example, the time from solstice to solstice, or equinox to equinox), is about 20 minutes shorter than the sidereal year, which is measured by the Sun's apparent position relative to the stars.
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An illustration of what Mars may have looked like during an ice age about 400,000 years ago caused by a large axial tilt As on Earth, the effect of precession causes the north and south celestial poles to move in a very large circle, but on Mars the cycle is 175,000 Earth years rather than 26,000 years as on Earth. As on Earth, there is a second form of precession: the point of perihelion in Mars's orbit changes slowly, causing the anomalistic year to differ from the sidereal year. However, on Mars, this cycle is 83,600 years rather than 112,000 years as on Earth. On both Earth and Mars, these two precessions are in opposite directions, and therefore add, to make the precession cycle between the tropical and anomalistic years 21,000 years on Earth and 56,600 years on Mars.
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A page from the Hindu calendar 1871-72 The Hindu calendar refers to a set of various lunisolar calendars that are traditionally used in the Indian subcontinent and South-east Asia, with further regional variations for social and Hindu religious purposes. They adopt a similar underlying concept for timekeeping based on sidereal year for solar cycle and adjustment of lunar cycles in every three years, however also differ in their relative emphasis to moon cycle or the sun cycle and the names of months and when they consider the New Year to start. Of the various regional calendars, the most studied and known Hindu calendars are the Shalivahana Shaka found in South India, Vikram Samvat (Bikrami) found in Nepal, North and Central regions of India, Tamil calendar used in Tamil Nadu – all of which emphasize the lunar cycle. Their new year starts in spring.
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De Sitter and Clemence both referred to the proposal as 'Newtonian' or 'uniform' time. D Brouwer suggested the name 'ephemeris time'.ESAA (1992), see page 79. Following this, an astronomical conference held in Paris in 1950 recommended "that in all cases where the mean solar second is unsatisfactory as a unit of time by reason of its variability, the unit adopted should be the sidereal year at 1900.0, that the time reckoned in this unit be designated ephemeris time", and gave Clemence's formula (see Definition of ephemeris time (1952)) for translating mean solar time to ephemeris time. The International Astronomical Union approved this recommendation at its 1952 general assembly.At the IAU meeting in Rome 1952: see ESAE (1961) at sect.1C, p. 9; also Clemence (1971). Practical introduction took some time (see Use of ephemeris time in official almanacs and ephemerides); ephemeris time (ET) remained a standard until superseded in the 1970s by further time scales (see Revision).
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Poul Anderson, who had a degree in physics, worked out the physical framework for the anthology based on the characteristics of HD36395 as they were known in the early 1990s: one third of Earth Sun's mass, 82% of its diameter, spectral type M1 with a photosphere temperature of 3,400 K and a maximum emission in the near infrared. (The star is in fact very similar to Gliese 581, now known to have a planetary system.) The twin terrestrial planets are separated by an average distance of only 156,000 km (about 40% of the Earth-Moon distance). They orbit around their center of mass in 91 hours in locked rotation, which minimizes the effects of the huge tidal forces which they exert on each other. This constellation orbits Murasaki within the habitable zone, at a distance of only 0.223 astronomical units (sidereal year, 66 Earth days) where the planets receive about the same amount of total irradiation Mars gets from the Sun; however, with a spectral power distribution shifted to much longer wavelengths.
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It can be established that SI seconds apply to this value by following the citation in "USEFUL CONSTANTS" to E. Groten "Parameters of Common Relevance of Astronomy, Geodesy, and Geodynamics" which states units are SI units, except for an instance not relevant to this value. Multiplying by (180°/π radians) × (86,400 seconds/day) yields , indicating that Earth rotates more than 360° relative to the fixed stars in one solar day. Earth's movement along its nearly circular orbit while it is rotating once around its axis requires that Earth rotate slightly more than once relative to the fixed stars before the mean Sun can pass overhead again, even though it rotates only once (360°) relative to the mean Sun.In astronomy, unlike geometry, 360° means returning to the same point in some cyclical time scale, either one mean solar day or one sidereal day for rotation on Earth's axis, or one sidereal year or one mean tropical year or even one mean Julian year containing exactly for revolution around the Sun.
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