Astrologers realize that over time the placement of constellations in the sky do change but the equinoxes remain the same and that is one of the main underlying factors of the current astrological system.
Two sites where you can get more information:
Kala Ambrose interviews Marguerite Manning http://www.examiner.com/metaphysical-spirituality-in-national/what-the-did-my-zodiac-sign-just-change
Jonathan Cainer brings his own thoughts to the table http://www.cainer.com/
We hope that this helps you settle any debates.