Home > Equatorial coordinate system
The equatorial coordinate system is probably the most widely used celestial coordinate system, whose equatorial coordinates are:
It is the most closely related to the geographic coordinate system, because they use the same fundamental plane, and the same poles. The projection of the Earth's equator onto the celestial sphere is called the celestial equator. Similarly, projecting the geographic poles onto the celestial sphere defines the north and south celestial poles.
There are two varieties:
- the hour angle system is fixed to the Earth like the geographic coordinate system
- the right ascension system rotates as the Earth does; it is fixed to the stars (actually, not quite, see precession) so it appears to rotate across the sky with the stars, but of course it's really the Earth rotating under the fixed sky.
The latitudinal (latitude-like) angle of the equatorial system is called declination (Dec for short). It measures the angle of an object above or below the celestial equator. The longitudinal angle is called the right ascension (RA for short). It measures the angle of an object east of the vernal equinox point. Unlike longitude, right ascension is usually measured in hours instead of degrees, because the apparent rotation of the equatorial coordinate system is closely related to sidereal timeSidereal time is time reckoned by sidereal days and is the time elapsed since a transit of the vernal equinox; this is, strictly, apparent sidereal time''. Mean sidereal time is reckoned not from the actual transit of the vernal equinox, but rather from t and hour angle. Since a full rotation of the sky takes 24 hours to complete, there are (360 degrees / 24 hours) = 15 degrees in one hour of right ascension.
This article originates from Jason Harris' Astroinfo which comes along with KStarsKStars is a planetarium program that runs under GNU/Linux and other Unix like operating systems. It is part of KDE. It provides an accurate graphical representation of the night sky, from any location on Earth, at any date and time. The display includes u, a Desktop Planetarium for LinuxThis article is about Linux-based operating systems, GNU/Linux, and related topics. See Linux kernel for the kernel itself. See Linux (washing powder) for the Swiss brand of washing powder. Tux, a plump penguin, is the official Linux mascot Linux is the n/ KDEKDE K D esktop E nvironment) is a free desktop environment and development platform built with Trolltech's Qt toolkit. It runs on most Unix and Unix-like systems, such as Linux, BSD and Solaris. There are also ports to Mac OS X using its X11 layer and Mic. See http://edu.kde.org/kstars/index.phtml
Celestial coordinate system
