Did Christianity arise from astrology and other religions, or was astrology woven into Christianity afterward?

I grew up as a Christian, but always had questions/doubts. I saw the Zeitgeist movie and it all seemed to make so much sense, the stated correlations between Christianity and astrology. Now I'm listening to Bill Cooper's "Mystery Babylon" series, among other research which states that these ideas were sort of retro-fitted for Christianity in order to gain acceptance from pagans at the time...and that these are the beliefs of the mystery schools, but it is a perversion of Christianity which has no base in astrology. Which is true? It all seems to fit so well, God's Sun, light of the world, born again, 12 disciples for 12 months, all grouped in 3's in The Last Supper for the 4 seasons, etc. etc...could all of that really be a lie? It seems like such a logical explanation. Thanks in advance for your help...references would be appreciated :-)