Longitude of the periapsis
From MedBib.com - Medicine & Nature
 |
This article may be confusing or unclear to readers. Please help clarify the article; suggestions may be found on the talk page. (July 2009) |
In astrodynamics, the longitude of the periapsis (symbolized 
) of an orbiting body is the longitude (measured from the point of the vernal equinox) at which the periapsis (closest approach to the central body) would occur if the body's inclination were zero. For motion of a planet around the sun, this position could be called longitude of perihelion. The longitude of periapsis is a compound angle, with part of it being measured in the plane of reference and the rest being measured in the plane of the orbit. Likewise, any angle derived from the longitude of periapsis (e.g. mean longitude and true longitude) will also be compound.
Sometimes, the term longitude of periapsis is used to refer to ω, the angle between the ascending node and the periapsis. That usage of the term is especially common in discussions of binary stars and exoplanets.[1] However, the angle ω is less ambiguously known as the argument of periapsis.
Calculation from state vectors
can be calculated from longitude of ascending node Ω and argument of periapsis ω:
which are derived from orbital state vectors.
References
- ^ See e.g. p. 201, The Binary Stars, Robert Grant Aitken, Semicentennial Publicaions of the University of California, 1918, or Format, Sixth Catalog of Orbits of Visual Binary Stars, William I. Hartkopf & Brian D. Mason, U. S. Naval Observatory, Washington, D.C. Accessed on line October 25, 2008
External links
- Determination of the Earth's Orbital Parameters Past and future longitude of perihelion for Earth.
This article is licensed under the GNU Free Documentation License.
All material adapted used from Wikipedia is available under the terms of the GNU Free Documentation License.
Seeking health information online: does Wikipedia matter?