Any circle that passes through the celestial poles is called an hour circle, and there are an infinite number of these circles. Each celestial object lies on an hour circle and is located on the celestial sphere by the coordinates of declination and right ascension. It is measured along the hour circle through the object and is expressed in angular units. Declination is similar to latitude on the Earth's surface. Latitude is measured north and south of the Earth's equator while declination is measured north and south of the celestial equator.
Right ascension is expressed in time units.
Right ascension is similar to longitude on the Earth's surface. Longitude is measured around the Earth's equator, and right ascension is measured around the celestial equator. The following table shows the right ascensions and declinations of a few celestial objects. The Sun's Yearly Motion One of the major advantages of the equatorial system is that the coordinates of stars are essentially independent of time and the observer's latitude. This is not true, however, for solar system objects.