For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
With respect to the previous answers, I find one is too esoteric to be of real use in casual conversation, and personally, would be interested to know the writer's source for his statements, as it is not commonly known. The other I find too passive and unhelpful in providing an alternative for the other person to consider.
Personally, when someone asks me that question, I return the question with one of my own, asking, "Do you really think our view of the arrangement of stars-inanimate balls of hot gas-- millions of light years away hold sway over the circumstances of our lives?" Mostly, they say, "no, not really, it just seems fun to think about it."
I then respond that it is a normal desire to have some knowledge of our coming future life events, however, I have found that entrusting my life to the one who created the stars, and everything else-including myself--and who knows me so intimately he has the hairs on my head numbered, is much more trustworthy than anything he has created for us to enjoy as a part of His beautiful creation.
of course, even this may be too complicated for the most casual encounters--and the simplest thing to say is, "I don't really think the stars have control over my destiny. That is something only God has control over--and since He created the stars--and everything else, I think I am pretty well covered."
Love in Christ,
I found this answer on a previous ebible question regarding zodiac and astrology to be most informative. I include the link here to that page: http://ebible.com/questions/1418?ori=352687