Right Ascension

These are coordinates on the celestial sphere, analogous to Latitude and Longitude on the surface of the earth. The difference is that Right Ascension does not rotate with the earth, as Longitude (which is tied to the Greenwich Meridian) does, but is measured with respect to a fixed point in the sky.
On the other hand, since the earth rotates around a fixed axis (to a pretty good approximation), the Declination and the Latitude are pretty much the same.