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Hence, for Earth, it is also the time taken for the Sun to return to the same position relative to Earth with respect to the fixed stars after apparently travelling once around the [[ecliptic]].
Hence, for Earth, it is also the time taken for the Sun to return to the same position relative to Earth with respect to the fixed stars after apparently travelling once around the [[ecliptic]].


It equals {{Nowrap|365.256 363 004 [[ephemeris day]]s}} for the [[Epoch (astronomy)#Julian years and J2000 |J2000.0]] epoch.{{Sfn|IERS|2014}} The sidereal year differs from the [[solar year]] (known also as "tropical year"), "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees",{{Sfn|AA|2016}} due to the [[Axial precession|precession of the equinoxes]].
It equals {{Nowrap|365.256 363 004 [[ephemeris day]]s}} for the [[Epoch (astronomy)#Julian years and J2000 |J2000.0]] epoch.{{Sfn|IERS|2014}} The sidereal year differs from the [[solar year]] (known also as tropical year), which is based on the sun's position in the sky and is "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees",{{Sfn|AA|2016}} due to the [[Axial precession|precession of the equinoxes]].
The sidereal year is 20 min 24.5 s longer than the mean solar year at J2000.0 {{Nowrap|(365.242 190 402 ephemeris days)}}.{{Sfn|IERS|2014}}
The sidereal year is 20 min 24.5 s longer than the mean solar year at J2000.0 {{Nowrap|(365.242 190 402 ephemeris days)}}.{{Sfn|IERS|2014}}


At present, the rate of [[axial precession]] corresponds to a period of 25,772 years, so sidereal year is longer than [[tropical year]] by 1,224.5 seconds (20 min 24.5 s, ~365.24219*86400/25772).
At present, the rate of [[axial precession]] corresponds to a period of 25,772 years, so sidereal year is longer than [[tropical year]] by 1,224.5 seconds (20 min 24.5 s, ~365.24219*86400/25772).


Before the discovery of the precession of the equinoxes by [[Hipparchus]] in the [[Hellenistic period]], the difference between
Before the discovery of the precession of the equinoxes by [[Hipparchus]] during the [[Hellenistic period]], the difference between
sidereal and tropical year was unknown.<ref>{{Cite web| last = Stern| first = David P.| title = Precession| work = NASA's Polar, Wind and Geotail Site| accessdate = April 25, 2022| date = October 10, 2016| url = https://pwg.gsfc.nasa.gov/stargaze/Sprecess.htm}}</ref> For naked-eye observation, the shift of the constellations
sidereal and solar year was unknown.<ref>{{Cite web| last = Stern| first = David P.| title = Precession| work = NASA's Polar, Wind and Geotail Site| accessdate = April 25, 2022| date = October 10, 2016| url = https://pwg.gsfc.nasa.gov/stargaze/Sprecess.htm}}</ref> For naked-eye observation, the shift of the constellations relative to the equinoxes only becomes apparent over centuries or "[[Astrological age|ages]]", and pre-modern calendars such as
relative to the equinoxes only becomes apparent over centuries or "[[Astrological age|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
[[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.{{Citation needed|date=August 2020}} The [[Indian national calendar]], based on the works of
of stars, effectively using the sidereal year.{{Citation needed|date=August 2020}} The [[Indian national calendar]], based on the works of
[[Maga Brahmin]]s, as are the calendars of neighbouring countries, is traditionally reckoned by the Sun's entry into the sign of
[[Maga Brahmin]]s, as are the calendars of neighbouring countries, is reckoned traditionally by the Sun's entry into the sign of
[[Aries (astrology)|Aries]] and is also supposed to align with the spring equinox and have relevance to the harvesting and planting
[[Aries (astrology)|Aries]] and is also supposed to align with the spring equinox and have relevance to the harvesting and planting
season and thus the tropical year.{{Citation needed|date=August 2020}} However, as the entry into the constellation occurs 25 days later,
season and thus the tropical year.{{Citation needed|date=August 2020}} However, as the entry into the constellation occurs 25 days later
according to the astronomical calculation of the sidereal year, this date marks the [[South and Southeast Asian solar New Year]] in
according to the astronomical calculation of the sidereal year, this date marks the [[South and Southeast Asian solar New Year]] in
other countries and cultures.{{Citation needed|date=August 2020}}
other countries and cultures.{{Citation needed|date=August 2020}}


Revision as of 01:19, 23 May 2023

A sidereal year (/saɪˈdɪəri.əl/, US also /sɪ-/; from Latin sidus 'asterism, star'), also called a sidereal orbital period, is the time that Earth or another planetary body takes to orbit the Sun once with respect to the fixed stars.

Hence, for Earth, it is also the time taken for the Sun to return to the same position relative to Earth with respect to the fixed stars after apparently travelling once around the ecliptic.

It equals 365.256 363 004 ephemeris days for the J2000.0 epoch.[1] The sidereal year differs from the solar year (known also as tropical year), which is based on the sun's position in the sky and is "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees",[2] due to the precession of the equinoxes. The sidereal year is 20 min 24.5 s longer than the mean solar year at J2000.0 (365.242 190 402 ephemeris days).[1]

At present, the rate of axial precession corresponds to a period of 25,772 years, so sidereal year is longer than tropical year by 1,224.5 seconds (20 min 24.5 s, ~365.24219*86400/25772).

Before the discovery of the precession of the equinoxes by Hipparchus during the Hellenistic period, the difference between sidereal and solar year was unknown.[3] 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.[citation needed] The Indian national calendar, based on the works of Maga Brahmins, as are the calendars of neighbouring countries, is reckoned traditionally by the Sun's entry into the sign of Aries and is also supposed to align with the spring equinox and have relevance to the harvesting and planting season and thus the tropical year.[citation needed] However, as the entry into the constellation occurs 25 days later according to the astronomical calculation of the sidereal year, this date marks the South and Southeast Asian solar New Year in other countries and cultures.[citation needed]

See also

Look up sidereal year in Wiktionary, the free dictionary.

Notes

  1. ^ a b IERS 2014.
  2. ^ AA 2016.
  3. ^ Stern, David P. (October 10, 2016). "Precession". NASA's Polar, Wind and Geotail Site. Retrieved April 25, 2022.

Works cited

  • "Glossary". Astronomical Almanac for the Year 2017. Washington, D.C. and London: United States Naval Observatory, HM Nautical Almanac Office. 2016. p. M19.
  • "Useful Constants". International Earth rotation and Reference systems Service (IERS). February 13, 2014. Retrieved February 29, 2020.
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