The Declination of a celestial object is its distance north or south of the celestial equator, measured in degrees, minutes and seconds of arc, on a great circle of the celestial sphere passing through the object and north and south poles of the heavens. These great circles are called hour circles and they correspond to the meridians or circles of longitude on the earth's surface. The declination of an object in the heavens corresponds to the latitude of a point on the earth's surface. The Right Ascension of a point on the celestial sphere corresponds to the longitude of a point on the earth's surface. It is measured--as longitude is measured--in degrees, minutes and seconds of arc or in hours, minutes and seconds of time--eastward along the celestial equator from the hour circle passing through the vernal equinox to the foot of the hour circle passing through the object. The hour circle passing through the vernal equinox is the zero meridian for the celestial sphere just as the meridian of Greenwich is the zero meridian on the earth's surface.