The orbital period is the time taken for a given object to make one complete orbit about another object.
When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.
There are several kinds of orbital periods for objects around the Sun (or other celestial objects):
- The sidereal period is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is considered to be an object's true orbital period.
- The synodic period is the temporal interval that it takes for an object to reappear at the same point in relation to two or more other objects, e.g., when the Moon relative to the Sun as observed from Earth returns to the same illumination phase. The synodic period is the time that elapses between two successive conjunctions with the Sun–Earth line in the same linear order. The synodic period differs from the sidereal period due to the Earth's orbiting around the Sun.
- The draconitic period, or draconic period, is the time that elapses between two passages of the object through its ascending node, the point of its orbit where it crosses the ecliptic from the southern to the northern hemisphere. This period differs from the sidereal period because both the orbital plane of the object and the plane of the ecliptic precess with respect to the fixed stars, so their intersection, the line of nodes, also precesses with respect to the fixed stars. Although the plane of the ecliptic is often held fixed at the position it occupied at a specific epoch, the orbital plane of the object still precesses causing the draconitic period to differ from the sidereal period.
- The anomalistic period is the time that elapses between two passages of an object at its periapsis (in the case of the planets in the solar system, called the perihelion), the point of its closest approach to the attracting body. It differs from the sidereal period because the object's semimajor axis typically advances slowly.
- Also, the Earth's tropical period (or simply its "year") is the time that elapses between two alignments of its axis of rotation with the Sun, also viewed as two passages of the object at right ascension zero. One Earth year has a slightly shorter interval than the solar orbit (sidereal period) because the inclined axis and equatorial plane slowly precesses (rotates in sidereal terms), realigning before orbit completes with an interval equal to the inverse of the precession cycle (about 25,770 years).
Other articles related to "period, orbital period, orbital periods, orbital":
... Synchronous orbit An orbit whose period is a rational multiple of the average rotational period of the body being orbited and in the same direction of ... Geosynchronous orbit (GSO) An orbit around the Earth with a period equal to one sidereal day, which is Earth's average rotational period of 23 hours, 56 ... When the orbit is circular and the rotational period has zero inclination, the orbit is considered to also be geostationary ...
... Orbital periods can be less than an hour (for AM CVn stars), or a few days (components of Beta Lyrae), but also hundreds of thousands of years (Proxima Centauri around Alpha Centauri AB) ...
... Binary star Orbital period AM Canum Venaticorum 17.146 minutes Beta Lyrae AB 12.9075 days Alpha Centauri AB 79.91 years Proxima Centauri - Alpha Centauri AB 500,000 ...
... According to general relativity, the short orbital period and high eccentricity should make the system an excellent emitter of gravitational radiation, thereby losing energy and decreasing the orbital period still ... The observed decrease in the orbital period over thirty years matches the predictions of general relativity within even the most precise measurements ... losing energy (averaged over a complete orbit) is given by where e is the orbital eccentricity and a is the semimajor axis of the elliptical orbit ...
... the planetary mass remains uncertain, with a range between 2 and 8 Earth masses, the radius and orbital period of COROT-7b are well constrained from COROT photometry it orbits very close to its star (1/23rd the ... A strong possibility exists that the planet's rotation is tidally locked to the orbital period, so that temperatures and geologic conditions on the sides of the planet facing ...
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