Editing Orbit equation (section)

{{Short description|Astrodynamic equation}}
In [[astrodynamics]], an '''[[orbit]] equation''' defines the path of [[orbiting body]] <math>m_2\,\!</math> around [[central body]] <math>m_1\,\!</math> relative to <math>m_1\,\!</math>, without specifying position as a function of time. Under standard assumptions, a body moving under the influence of a force, directed to a central body, with a magnitude inversely proportional to the square of the distance (such as gravity), has an orbit that is a [[conic section]] (i.e. [[circular orbit]], [[elliptic orbit]], [[parabolic trajectory]], [[hyperbolic trajectory]], or [[radial trajectory]]) with the central body located at one of the two [[Focus (geometry)|foci]], or ''the'' focus ([[Kepler's laws of planetary motion#Kepler.27s first law|Kepler's first law]]).

If the conic section intersects the central body, then the actual trajectory can only be the part above the surface, but for that part the orbit equation and many related formulas still apply, as long as it is a [[freefall]] (situation of [[weightlessness]]).