Sidereal period
Sidereal period ( latin sidus 'Stern' , genitive sideris ) is in astronomy the time for a complete revolution ( rotation ) or for a complete revolution ( revolution ) of a celestial body with respect to the fixed star background . The sidereal period of revolution of a celestial body is also rotation period or sidereal day called the sidereal period of his round and round trip time , period of revolution or sidereal year.
- A sidereal day on earth is shorter than a civil day (mean solar day ), since during a complete orbit around the sun with respect to the starry sky (sidereal), the earth completes exactly one complete revolution more than those with respect to the sun ( synodic ) the change between day and night become visible.
- The tropical period, called a sidereal day , is also a little shorter because here the spring equinox is not fixed as a reference point like a fixed star, but shifts in opposite directions - in the precession cycle by 360 degrees in 25,800 years, i.e. 0.014 degrees = 50 arc seconds per year .
- A sidereal year corresponds to the duration of a complete orbit of a planet through the zodiac from one fixed star position until it reaches the same position again. The name is derived from sidus "star", since one complete revolution corresponds to the recurring culmination of a fixed star at a certain (but arbitrary) place on the planet.
- In relation to the earth, a sidereal year is about 20 minutes longer than a civil year , because the earth follows the apparent movement of the sun due to precession . The difference to the tropical year is 20 min 24 s.
The sidereal month is the mean time until the moon appears again in front of the same fixed star when viewed from the earth. This period lasts about 27,322 days (see also lunar orbit ); other definitions of "month" are:
- A synodic month ( lunation ) is the duration until the moon is again in the same elongation to the earth, for example from new moon to new moon.
- A tropical month refers to the vernal equinox as a reference point.
- A Draconite month refers to the passages through the same lunar node ( Draconite period ).
- An anomalous month is the period of two periods of perigee ( anomalous period ).
Sidereal periods in the solar system
The following table gives the duration periods of the sidereal planets of the solar system , of a body in the asteroid belt (Ceres) and Trans Neptunes (Pluto, Quaoar and Sedna) in ( SI ) days and calendar years of:
| object | sidereal period | |
|---|---|---|
| Mercury | 87,969 days | 0.241 years |
| Venus | 224,701 days | 0.615 years |
| Earth E1 | 365.256 days | 1 (sidereal) year |
| Mars | 686,980 days | 1,881 years |
| Ceres | 1,682.00 days | 4.605 years |
| Jupiter | 4,332.66 days | 11,862 years |
| Saturn | 10,759.7 days | 29,458 years |
| Uranus | 30,686.6 days | 84.014 years |
| Neptune | 60,191.6 days | 164.793 years NP |
| Pluto | ≈248.2 years NP | |
| Quaoar | ≈285.09 years | |
| Sedna | ≈11,700 years | |
- E1For the orbital period of the earth see earth orbit
- NPThe orbital periods of Neptune and Pluto are so long that modern astronomy has not yet fully grasped them. The values given are based on planetary theories (such as the VSOP 87 ), which then provide useful results in model calculations. The confirmation by measurement is still pending. On April 11, 2009, Neptune completed its first fully observed period, and can be given relatively accurately.
(For a tabular comparison with their synodic periods, see also table: Orbital times in the solar system )
Web links
- Sidereal (lexicon entry). In: Meyers Großes Konversations-Lexikon. 6th edition, Bibliographisches Institut, Leipzig / Vienna 1905-1909. 1909, Retrieved July 9, 2018 .
- Year (lexicon entry). In: Meyers Großes Konversations-Lexikon. 6th edition, Bibliographisches Institut, Leipzig / Vienna 1905-1909. 1909, Retrieved July 9, 2018 .