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The '''orbital period''' of any [[planet]] or [[moon]] is the time required to complete an [[orbit]].<ref>Braeunig, Robert A. "[http://www.braeunig.us/space/orbmech.htm Basics of Space Flight: Orbital Mechanics]." Rev. ed. 2007. Accessed January 11, 2008.</ref>

== Types of orbital period ==
"Completion of an orbit" has many definitions. In consequence, many definitions of orbital period are known to [[Astronomy|astronomers]].

* The ''sidereal period'' is the time required for a body to make one circuit around its primary with respect to the stars. It is the truest definition of an orbital period. In fact it is what is meant by "orbital period" whenever one uses the latter term without qualification.
* The ''synodic period'' is the time required for a body to reach the same position in the sky of [[earth]], in relation to the [[Sun]]. Hence for any body except the earth itself, sidereal and synodic years are quite different, for the simple reason that the earth has an orbit of its own. Planets and other bodies beyond the earth have a synodic year longer than the earth year, but as an object's [[semi-major axis]] lengthens, its synodic year approaches the earth year.
* The ''draconitic period'' is the time between two passages of the object through the ''ascending node'' of its orbit (the point at which the satellite passes from the south to the north of its primary's equatorial plane).
* The ''anomalistic period'' is the time between two passages through [[apsis|periapsis]], the point of the object's closest approach to its primary.
* The ''tropical period'' is the time between two passages of the object through a [[right ascension]] of zero.

In addition to the above, the period of any [[planet]] or [[dwarf planet]] or other satellite of the [[Sun]] is called a ''year''. The period of a natural [[satellite]] is called a ''month'' (from ''moonth'').

== References ==
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[[Category:Astronomy]]