In
astronomy, the
hour circle of a celestial object is the
great circle through the object and the
celestial poles. It is perpendicular to the
celestial equator. The declination of an object as observed on the celestial sphere is the angle measured along the hour circle of that object to the celestial equator. In other words, it is analogous to meridians or longitudes on a globe. A
meridian on the celestial sphere matches an hour circle at any time.