Hello pf, I have been trying to grasp the concept of RA. I have read through a few books and I know that it is measured eastwards from the point on the celestial sphere where the Sun crosses the celestial equator at the vernal equinox. I just want to check I understand this correctly. Does it mean when the Sun cross the celestial equator, whatever star happens to be behind the Sun at that point would serve as a RA of zero? My other query is whenever you look up right ascensions on the internet or a phone app they are always constantly changing (or at least for planets)? Again I tried to research this with little luck but is it because nearby objects e.g. planets appear to not stay at the same point in the sky day to day because the Earth moves around the Sun (which is why a solar day is 4 minutes longer). So a planet would change its right ascension by 4 minutes each day? But a star is so much further away it will be fixed? Any help is much appreciated.