The equatorial system is in many respects similar to the geographical coordinate system of latitude and longitude. Circles through the North and South Poles are called circles of longitude while circles through the north and south celestial poles are called hour circles . 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.