Declination measures how high a star is in the sky. Declination of an object is the angular distance north or south of the celestial equator. For example, a star that appears on the north celestial pole has a declination of 90 o degrees and a star on the celestial equator has a declination of 0 o whereas a star on the south celestial pole has a declination of -90 o . Right ascension measures where a star is positioned around the celestial sphere. The right ascension of an object is the angular distance from the vernal equinox eastward.
Right ascension is measured in hours, minutes and seconds.
One hour is 15 degrees. In order to locate an object in the sky you must know both its right ascension and its declination. This is analagous to finding a city on the Earth using latitude and longitude. N latitude and 86.5 o W longitude. Now that we know about the celestial sphere we need to understand the celestial motions of the objects in the night sky.