Ascension Right

Ascension, Right, one of the arcs required to express the position of a heavenly body in the celestial sphere. It corresponds to the longitude of a place on the earth's surface, and with a knowledge of the declination, which corresponds to latitude, the exact position of the body is determinate. Just as terrestrial longitude requires some fixed meridian, such as that through Greenwich, as a standard from which to measure the position of other meridians, so must there be a fixed declination circle or meridian in the heavens, from which the right ascension of any star shall be measured. The point on the celestial equator through which this standard declination circle passes is known as the first point in Aries. Right ascension may be expressed as an angle in degrees, minutes, and seconds, or as the sidereal time taken for the object to culminate, reckoned from the instant the first point in Aries traverses the meridian.