The Signs of the Zodiac: 
Ancient astrologers thought of the sky which surrounds us as a giant
sphere, of which the earth is the center. Only the movements of the
visible stars count: the sun, moon, and the eight known plantets rotate
around at greater or lesser distances and at varying speeds. The sun,
moon, Mercury, Venus and Mars, relatively close to us, move rapidly;
Jupiter, Saturn, Uranus, Neptune, and Pluto rotate slowly as they
are further away.
But all follow their regular orbits within a zone of approximately
17 degrees width. This belt is known as the zodiac, its elliptical
line is known as the ecliptic. It is a large circle which the sun
will trace over the period of a year, moving about one degree a day.
The elliptical plane is tilted 23 degrees 27' from the plane of the
celestial equator; it is therefore not perpendicular at the poles
of the earth's axis. The point at which the elliptical plane crosses
the celestial equator is the "gamma" point. The sun crosses
the gamma point onf the 21st of March, the vernal equinox.
Like every circle, the ring which circumscribes the zodiac is divisible
into 360 degrees; these are divided into twleve equal sections of
30 degrees each; the signs of the zodiac.
Being born "under the sign of Aries" means that at the moment
of birth, the sun was located somewhere between the first and the
thirtieth degree of the sign of Aries.
Because the sun moves forward by approximately one degree per day,
it takes one month for the sun to cross a sign. The zodiac year beginning
on the 21st of March, the sun crosses, in successsion:
Aries, from March 21st to April 21st
Taurus, from April 22nd to May 21st
Gemini, from May 22nd to June 21st
Cancer, from June 22nd to July 21st
Leo, from July 22nd to August 21st
Virgo, from August 22nd to September 21st
Libra, from September 21st to October
23rd
Scorpio, from October 24th to November
22nd
Sagittarius, from November 23rd to December
21st
Capricorn, from December 22nd to January
20th
Aquarius, from January 21st to February
18th
Pisces, from February 19th to March 20th
Astrology includes all of the stars of the solar system, including
the planets and even the sun and the moon, even though they are less
well known, their symbolism is as detailed as that of the signs of
the zodiac.
Note, however, that, depending on the year, the sun may pass through
these signs with one or two days difference.
By tradition, the twelve signs are grouped into categories of the
four elements: fire, air, earth, and water. Tradition also holds that
for each sign there is : A planet : Aries is ruled by Mars, Taurus
by Venus, etc.