Orbital speed

In <a href="/facts/Gravitational_binding_energy/sQYcuUll">gravitationally bound</a> systems, the orbital speed of an <a href="/facts/Astronomical_object/BCHLa0Q2">astronomical body</a> or object (e.g. <a href="/facts/Planet/rbPjE6Bx">planet</a>, <a href="/facts/Natural_satellite/AE4KQKbq">moon</a>, <a href="/facts/Satellite/PTX8c68t">artificial satellite</a>, <a href="/facts/Spacecraft/YQqQaUw0">spacecraft</a>, or <a href="/facts/Star/PFbd6ICx">star</a>) is the <a href="/facts/Speed/I3qgMPfs">speed</a> at which it <a href="/facts/Orbit/nD2TPySG">orbits</a> around either the <a href="/facts/Barycenter/Fw9renao">barycenter</a> (the combined center of mass) or, if one body is much more massive than the other bodies of the system combined, its speed relative to the <a href="/facts/Center_of_mass/n4Lr9GAz">center of mass</a> of the <a href="/facts/Primary_body/PzvXx42a">most massive body</a>.
The term can be used to refer to either the mean orbital speed (i.e. the average speed over an entire orbit) or its instantaneous speed at a particular point in its orbit. The maximum (instantaneous) orbital speed occurs at <a href="/facts/Apsis/VaL6ow9w">periapsis</a> (perigee, perihelion, etc.), while the minimum speed for objects in closed orbits occurs at apoapsis (apogee, aphelion, etc.). In ideal <a href="/facts/Two-body_problem/YCG4geSH">two-body systems</a>, objects in open orbits continue to slow down forever as their distance to the barycenter increases. 
When a system approximates a two-body system, instantaneous orbital speed at a given point of the orbit can be computed from its distance to the central body and the object's <a href="/facts/Specific_orbital_energy/TvB2yk8a">specific orbital energy</a>, sometimes called "total energy". Specific orbital energy is constant and independent of position.

Orbital speed open-in-new

Orbital speed