Fig7_2 Celestial coords

Fig7_2 Celestial coords

Fig. 7.2 . Stars, galaxies and other cosmic objects are placed upon an imaginary celestial sphere. The celestial equator divides the sphere into northern and southern halves, and the ecliptic is the annual path of the Sun on the celestial sphere. The celestial equator intersects the ecliptic at the Vernal Equinox and the Autumnal Equinox. Every cosmic object has two celestial coordinates. They are the right ascension, designated by the angle alpha, a, or by R.A., and the declination, denoted by the angle delta, d, or Dec.. Right ascension is measured eastward along the celestial equator from the Vernal Equinox to the foot of the great circle that passes through the object. Declination is the angular distance from the celestial equator to the object along the great circle that passes through the object, positive to the north and negative to the south. Precession results in a slow motion of the Vernal Equinox, producing a steady change in the celestial coordinates.

Copyright 2010, Professor Kenneth R. Lang, Tufts University