Editing Synchronous orbit

{{Short description|Orbit of an astronomical body equal to that body's average rotational period}}
A '''synchronous orbit''' is an [[orbit]] in which an orbiting body (usually a [[satellite]]) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body.<ref>{{Cite web|url=http://earthobservatory.nasa.gov/Features/OrbitsCatalog/|title=Catalog of Earth Satellite Orbits : Feature Articles|last=Holli|first=Riebeek|date=2009-09-04|website=earthobservatory.nasa.gov|language=en|access-date=2016-05-08}}</ref>

== Simplified meaning ==
A [[synchronous]] [[orbit]] is an orbit in which the orbiting object (for example, an artificial satellite or a moon) takes the same amount of time to complete an orbit as it takes the object it is orbiting to rotate once.

== Properties ==
A satellite in a synchronous orbit that is both [[equator]]ial and [[circle|circular]] will appear to be suspended motionless above a point on the orbited planet's equator. For synchronous satellites orbiting [[Earth]], this is also known as a [[geostationary orbit]]. However, a synchronous orbit need not be equatorial; nor circular. A body in a non-equatorial synchronous orbit will appear to oscillate north and south above a point on the planet's equator, whereas a body in an [[ellipse|elliptical]] orbit will appear to oscillate eastward and westward. As seen from the orbited body the combination of these two motions produces a figure-8 pattern called an [[analemma]].

== Nomenclature ==
There are many specialized terms for synchronous orbits depending on the body orbited. The following are some of the more common ones. A synchronous orbit around [[Earth]] that is circular and lies in the equatorial plane is called a [[geostationary orbit]]. The more general case, when the orbit is inclined to Earth's equator or is non-circular is called a [[geosynchronous orbit]]. The corresponding terms for synchronous orbits around [[Mars]] are [[Areostationary orbit|areostationary]] and [[Areosynchronous orbit|areosynchronous]] orbits. {{citation needed|date=November 2019}}

== Formula ==

For a stationary synchronous orbit:

: <math>R_{syn} = \sqrt[3]{{G(m_2)T^2\over 4 \pi^2}}</math><ref>{{Cite news|url=https://www.askwillonline.com/2012/12/calculating-radius-of-geostationary.html|title=Calculating the Radius of a Geostationary Orbit - Ask Will Online|date=2012-12-27|work=Ask Will Online|access-date=2017-11-21|language=en-GB}}</ref>
: G = [[Gravitational constant]]
: m<sub>2</sub> = Mass of the celestial body
: T = rotational period of the body
:<math>R_{syn}</math> = Radius of orbit

By this formula one can find the stationary orbit of an object in relation to a given body.

Orbital speed (how fast a satellite is moving through space) is calculated by multiplying the angular speed of the satellite by the orbital radius.<ref>see [[Circular motion#Formulas]]</ref>

== Examples ==
An astronomical example is [[Pluto]]'s largest moon [[Charon (moon)|Charon]].<ref>{{cite journal |title = The Pluto-Charon system |author = S.A. Stern |year = 1992 |journal = Annual Review of Astronomy and Astrophysics |volume = 30 |page = 190 |quote=Charon's orbit is (a) synchronous with Pluto's rotation and (b) highly inclined to the plane of the ecliptic. |bibcode=1992ARA&A..30..185S|doi = 10.1146/annurev.aa.30.090192.001153 }}</ref>
Much more commonly, synchronous orbits are employed by artificial satellites used for communication, such as [[geostationary satellites]].

For natural satellites, which can attain a synchronous orbit only by [[tidal locking|tidally locking]] their parent body, it always goes in hand with [[synchronous rotation]] of the satellite. This is because the smaller body becomes tidally locked faster, and by the time a synchronous orbit is achieved, it has had a locked synchronous rotation for a long time already.{{citation needed|date=November 2011}}

{| class="wikitable sortable"
|-
! Orbit !! Body's Mass (kg) !! Sidereal Rotation period !! Semi-major axis (km) !! Altitude
|-
| [[Geostationary orbit]] ([[Earth]]) || 5.97237×10<sup>24</sup> || 0.99726968 d || {{cvt|42,164|km}} || {{cvt|35,786|km}}
|-
| [[areostationary orbit]] ([[Mars]]) || 6.4171×10<sup>23</sup> || 88,642 s || {{cvt|20,428|km}} || {{cvt|17032|km}}
|-
| [[Ceres (dwarf planet)|Ceres]] stationary orbit || 9.3835×10<sup>20</sup> || 9.074170 h || {{cvt|1192|km}} || {{cvt|722|km}}
|-
| [[Pluto]] stationary orbit ||1.3025×10<sup>22</sup> || 6.38680 d|| {{cvt|18857|km}} || {{cvt|16480|km}}
|}

== See also ==
* [[Subsynchronous orbit]]
* [[Supersynchronous orbit]] 
* [[Graveyard orbit]]
* [[Tidal locking]] (synchronous rotation)
* [[Sun-synchronous orbit]]
* [[List of orbits]]

==References==
{{reflist}}
* {{FS1037C}}

{{orbits|state=expanded}}

[[Category:Astrodynamics]]
[[Category:Orbits]]