Editing Mean anomaly (section)

{{Short description|Specifies the orbit of an object in space}}
[[File:Mean anomaly diagram.png|thumb|upright=1.2|Area swept out per unit time {{colorbox|lightgrey}}{{nbsp}}by an object in an [[elliptic orbit|elliptical orbit]], and {{colorbox|pink}}{{nbsp}}by an imaginary object in a [[circular orbit]] (with the same orbital period). Both sweep out equal areas in equal times, but the angular rate of sweep varies for the elliptical orbit and is constant for the circular orbit. Shown are '''mean anomaly''' and [[true anomaly]] for two units of time. (Note that for visual simplicity, a non-overlapping circular orbit is diagrammed, thus this circular orbit with same orbital period is not shown in true scale with this elliptical orbit: for scale to be true for the two orbits of equal period, these orbits must intersect.)|alt=]]
{{Astrodynamics}}
In [[celestial mechanics]], the '''mean anomaly''' is the fraction of an [[elliptic orbit|elliptical orbit's]] period that has elapsed since the orbiting body passed [[apsis|periapsis]], expressed as an [[angle]] which can be used in calculating the position of that body in the classical [[two-body problem]]. It is the angular distance from the [[apsis|pericenter]] which a fictitious body would have if it moved in a [[circular orbit]], with constant [[speed]], in the same [[orbital period]] as the actual body in its elliptical orbit.<ref>
{{cite book 
 | last = Montenbruck
 | first = Oliver
 | title = Practical Ephemeris Calculations
 | url = https://archive.org/details/practicalephemer00mont
 | url-access = limited
 | publisher = [[Springer-Verlag]]
 | year = 1989
 | isbn = 0-387-50704-3
 | page = [https://archive.org/details/practicalephemer00mont/page/n52 44]
}}</ref><ref>
{{cite book 
 | last = Meeus
 | first = Jean
 | title = Astronomical Algorithms
 | url = https://archive.org/details/astronomicalalgo00meeu_597
 | url-access = limited
 | publisher = Willmann-Bell, Inc., Richmond, VA
 | year = 1991
 | ISBN = 0-943396-35-2 
 | page = [https://archive.org/details/astronomicalalgo00meeu_597/page/n186 182]
}}</ref>