The orbital period or revolution period in astronomy is the time in which a celestial body completes its orbit around a reference point (has passed through its orbit once), i.e. the duration of a revolution.
It should be noted that there can be different reference points to which the complete 360 ° circuit is measured. B. the period of revolution of the moon with or without taking into account the simultaneous movement of the earth around the sun .
- Either the starry sky is used for this , such an orbital period is called the sidereal period (relative to the stars).
- Or the orbital time is measured in the plane of the orbit in relation to the pericenter (the point of the orbit ellipse closest to the center), that is the anomalistic period , the orbital period , as it results from the third Kepler law .
- The tropical period is particularly important for the earth , it takes into account the drift of the vernal equinox , which is the base reference point for all geocentric coordinate systems
- For long-term calculations of galaxies , their center is decisive, for example the galactic center ( galactic coordinate system ) for the Milky Way .
The reference can also be the (apparent) position of the sun ( synodic period ), the knot of individual planetary orbits ( draconic period ), the center of gravity of the entire solar system , its total center of mass ( barycentric period ) or the "rest of the universe " (see inertial system ).
Table: Orbital times in the solar system
In the special case of the earth's orbit around the sun, the length of the revolution period is one year ; this expression is generalized, for example to a "Mars year", a "Venus year" etc.
The orbital times follow Newton's law of gravitation :
- U is the period of revolution,
- a is the semi-major axis ,
- M 1 and M 2 are the masses of the central body and the satellite,
- G is the gravitational constant .
The orbital times of the planets are related to one another according to Kepler's third law :
- The squares of the periods of revolution are in the same ratio as the cubes of the major semi-axes.
The following table contains the times for the synodic, sidereal or anomalistic periods of rotation of the planets of the solar system , a body in the asteroid belt and of trans-Neptunes , as well as the earth's moon, satellites and the sun (given in days and calendar years ):
- Except for the Earth's moon, the difference between the anomalistic orbital period and the sidereal orbital period is negligible in this accuracy, because the pericentres of the planets and asteroids shift only minimally compared to the period of orbit ( pericenter rotation ).
- In contrast to the moon, the synodic orbital times for Mercury and Venus are significantly longer , but for Mars and the outer planets (the term “inside / outside” refers to the asteroid belt, not the earth), it is increasingly shorter . The exact explanation for this see in the section Planets of the article Synodic Orbital Period .
|object||Sidereal anomalous orbital period
"in relation to the fixed stars / the orbit geometry"
"in relation to earth and sun"
|ISS||I11.51 hours||I21.53 hours|
|Geosynchronous||G123.93 hours||24.00 hours|
27,322 days / |
27,554 days M2
|Mercury||87,969 days||115.88 days|
|Venus||224,701 days||583.92 days|
|Earth E1||365.256 days||-|
|Mars||686,980 days||779.94 days|
|Ceres||4.605 years||466.72 days|
|Jupiter||11,862 years||398.88 days|
|Saturn||29,458 years||378.09 days|
|Uranus||84.014 years||369.66 days|
|Neptune||164.793 years||367.49 days|
|Pluto||NP≈247.94 years||366.73 days|
|Quaoar||NP≈285.09 years||366.54 days|
|Sedna||≈10704 NPyears||365.29 days|
|Sun S||≈230 million years||-|
Conversion synodic - sidereal
- = sidereal period of revolution of the earth
Table: Orbit times of the sun, moon, earth and derived time quantities
|Sidereal day||Sidereal Month (1)||Sidereal year|
|86164,099s||27.32166 d||365.256366 d|
|23h 56m 4.099s||27d 7h 43m 11.5s||365d 6h 9m 9s|
|Sidereal day (2)||Tropical month||Tropical year|
|86164.091 s||27.32158 d||365.242199 d|
|23h 56m 4.091s||27d 7h 43m 4.7s||365d 5h 48m 46s|
|Sunny day (3)||Synodic month (5)||Solar year (3)|
|86400s (4)||29.53059 d||365.242199 d (6)|
|24h (4)||29d 12h 44m 2.9s||365d 5h 48m 46s (6)|
|Calendar day||Calendar month||Calendar year (8)|
|1 d = 86400 s (7)||30 d / 31 d||365.2425 d|
|24h (7)||365d 5h 49m 12s|
- Gerhard Dangl: ISS - Visibility table July 22, 2009 to July 25, 2009. Retrieved on August 5, 2009 .