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There are several kinds of orbital periods for objects around the Sun:

• The sidereal period is the time that it takes the object to make one full orbit around the sun, relative to the stars. This is considered to be an object's true orbital period.
• The synodic period is the time that it takes for the object to reappear at the same spot in the sky, relative to the Sun, as observed from Earth. This is the time that elapses between two successive conjunctions with the sun and is the object's Earth-apparent orbital period. The synodic period differs from the sidereal period since Earth itself revolves around the sun.
• The draconitic period is the time that elapses between two passages of the object at its ascending node, the point of its orbit where it crosses the ecliptic from the southern to the northern hemisphere. It differs from the sidereal period because the object's line of nodes typically precesses or recesses slowly.
• The anomalistic period is the time that elapses between two passages of the object at its perihelion, the point of its closest approach to the Sun. It differs from the sidereal period because the object's semimajor axis typically precesses or recesses slowly.
• The tropical period, finally, is the time that elapses between two passages of the object at right ascension zero. It is slightly shorter than the sidereal period because the vernal point precesses.

1 Relation between sidereal and synodic period

Using the abbreviations

E = the sidereal period of Earth (a sidereal yearThe sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. The sidereal year is the orbital period of Earth. A sidereal year equals 365. 2564 mean solar days. The sidereal year is 20 minutes a, not the same as a tropical yearA 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 precise length of time depends on which point of the ecliptic one)

P = the sidereal period of the other planet

S = the synodic period of the other planet (wrt Earth)

During the time S, the Earth moves over an angle of ( 360°This article describes "degree" as a unit of angle. For alternative meanings, see Degree (disambiguation). A degree of arc usually symbolized by the symbol °, is a measurement of plane angles, or of a location along a great circle of a sphere (such as the/E)S (assuming a circular orbit) and the planet moves (360°/P)S.

Let us consider the case of an inferior planet, i.e. a planet that will complete one orbit more than Earth before the two return to the same position relative to the sun.

and using algebraAlgebra Algebra (from the Arabic al-jabr meaning reunion connection or completion is a branch of mathematics which may be roughly characterized as a generalization and extension of arithmetic; it also refers to a particular kind of abstract algebra struct we obtain

For a superior planet one derives likewise:

The above formulæ are easily understood by considering the angular velocities of the Earth and the object: the object's apparent angular velocity is its true (sidereal) angular velocity minus the Earth's, and the synodic period is then simply a full circle divided by that apparent angular velocity.

Table of synodic periods in the Solar System, relative to Earth: