There are different astrological charts being used today. It is believed the Babylonians developed the first astrological and astronomical charts around the 2nd millennium B.C. They created the 12 houses of the zodiac which represent different areas of our lives. This chart gave birth to different systems of piecing together a horoscope.
Western astrology is based on the Tropical zodiac. This system is based on the Earth's position to the sun. What that means is our signs are based on the seasons not the star constellations. There are 12 houses, more commonly called signs. The start of the House of Aries is fixed to the spring equinox and the other signs follow in order of procession.
But, it's the stars that have changed, not the seasons, due to the gravitational pull of the moon which has made the Earth wobble on its axis. Our perspective of the stars is no longer the same since those first charts were drawn in ancient Babylonia.
Star astrologists work by the sidereal zodiac, which is more popular in Eastern cultures. They use astrological charts based on the constellations in the sky. Because the constellations are continuously changing due to the tilt of the Earth, the dates for this zodiac change, too. These are the astrologists that are most effected by the inclusion of the 13th sign called Ophiuchus, pronounced (Ooh-FEE-yew-kus), and known as the Serpent Bearer. This sign was discarded by the Babylonians because they wanted an even number for an equal-house zodiac. Tradition has basically stayed the same even though astronomers and astrologists knew of Ophiuchus's placement.
|Tropical Zodiac||Sidereal Zodiac ||Updated Sidereal|
|Aries||Mar 21-Apr 20||Apr 15-May 15||Apr 18-May 13|
|Taurus||Apr 21-May 21||May 16-June 15||May 13-June 21|
|Gemini||May 22-June 21||June 16-July 16||June 21-July 20|
|Cancer||June 22-July 23||July 16-Aug15||July 20-Aug 10|
|Leo||July 24-Aug 23||Aug 16-Sept 15||Aug 10-Sept 16|
|Virgo||Aug 24-Sept 23||Sept 16-Oct 15||Sept 16-Oct 30|
|Libra||Sept 24-Oct 23||Oct 16-Nov 15||Oct 30-Nov 23|
|Scorpio||Oct 24-Nov 22||Nov 16-Dec 15||Nov 23-Nov 29|
|Ophiuchus|| ||Nov 29-Dec 17|
|Sagittarius||Nov 23-Dec 21||Dec 16-Jan 14||Dec 17-Jan 20|
|Capricorn||Dec 22-Jan 20||Jan 15-Feb 14||Jan 20-Feb 16|
|Aquarius||Jan 21-Feb 19||Feb 14-Mar 14||Feb 16-Mar 11|
|Pisces||Feb 20-Mar 20||Mar 15-Apr 14||Mar 11-Apr 18|
This information is as accurate as I can make it from my research. The sidereal dates are always changing and I had some difficulty in locating dates to compare with the current set without doing the mathematical calculations myself. The set I used here are from charts I found from 2002. I wanted to demonstrate the difference in the movement of the star constellations. Any mistakes made are my own.