Astrology is based on what constellation the sun was in at the time of your birth. One thing it doesn't take into account is precession. The Earth actually wobbles a bit, like a spinning top that is slowing down. OK, so it takes 25,800 years each wobble, but it's still there. Have you ever heard that Polaris wasn't the north star when the pyramids were built? Same idea. Precession causes the date that the sun is at a particular point in the Zodiac to slip about one day every 70 years.
Another problem is that all of the zodiacal constellations aren't the same size. There's also a 13th one, Ophiucus, which isn't even recognized by astrologers. Here's a table that explains things better:
Constellation Traditional Actual(2000) Days Capricornus Dec 22-Jan 21 Jan 21-Feb 16 26 Aquarius Jan 22-Feb21 Feb 16-Mar 11 24 Pisces Feb 22-Mar 21 Mar 11-Apr 18 38 Aries Mar 22-Apr 21 Apr 18-May 13 25 Taurus Apr 22-May 21 May 13-Jun 22 40 Gemini May 22-Jun 21 Jun 22-Jul 21 29 Cancer Jun 22-Jul 21 Jul 21-Aug 10 20 Leo Jul 22-Aug 21 Aug 10-Sep 16 37 Virgo Aug 22-Sep 21 Sep 16-Oct 31 45 Libra Sep 22-Oct 21 Oct 31-Nov 23 23 Scorpius Oct 22-Nov 21 Nov 23-Nov 29 6 Ophiucus Not listed Nov 29-Dec 18 19 Sagittarius Nov 22-Dec 21 Dec 18-Jan 21 34 Days lists the number of days the sun is in each constellation.In short, astrology is all a bunch of hooey!
Information for this page was obtained in the June 1998 issue of Sky and Telescope magazine.
All this time I thought I was an Aries, but I'm really a Pisces! HA!
Here is an illustration. April 6th is just about in the center of the Aries astrological sign (March 22 - April 21). Look at where the Sun is on that date. It is smack in the middle of Pisces.
Here it is on the same date in the year 0000