The New Student's Reference Work/Ascension, Right

Ascension, Right, in astronomy, a term used with declination (tending down or aside), for defining the position of points of the celestial concave and indicating their positions relative to each other, right ascension being measured on the equinoctial from the first point of Aries eastward, while declination measures the secondaries of the equinoctial to the north and south poles of the heavens from 0 to 90. Right ascension, which is commonly expressed in time, one hour corresponding to 15⁰ on the celestial sphere, is invariably measured from west to east, thus corresponding to longitude on the earth, while declination corresponds to latitude. The right ascension of a star or other heavenly body is ascertained by a transit instrument and a clock.