-
Notifications
You must be signed in to change notification settings - Fork 2
Coordinate Systems
Definitions of coordinate systems in use in CppEphem code:
The definitions below are borrowed from the SOFA documentation.
The Celestial Intermediate Reference System (CIRS) represents a coordinate system centered on the Earth's center. Because of this, the coordinates of an object in CIRS are not fixed with respect to time and will change slightly from night to night due to the motion of the Earth around the Sun.
The International Celestial Reference System (ICRS) represents a coordinate system centered at the barycenter of the solarsystem. It is the IAU standard for celestial positions. This coordinate system was setup to be within about 25 milliarcseconds of the J2000 mean RA,Dec. Read more on the Wikipedia page.
Galactic longitude (l) and latitude (b) coordinates reference the direction along the observed Galactic plane. More details are provided on the Wikipedia page.
Observed altitude and zenith coordinates represent an observer's local sky coordinates. Azimuth is defined such that due North = 0 degrees, East = 90 degrees, South = 180 degrees and West is 270 degrees. The zenith angle is defined such that zenith is 0 degrees and increases towards the horizon. Altitude may be calculated from zenith via
altitude = 90 - zenith
Implemented as the mean barycentric ecliptic longitude and latitude. This does not take into account small perturbations from the nutation of the planet.
© Joshua V. Cardenzana, all rights reserved