The zodiac is a band of sky around the celestial sphere about eighteen degrees in width, tilted at an angle of 23.5 degrees relative to the Earth’s equator. It is centred on the ecliptic, the Sun’s apparent path around the Earth (so called because eclipses occur along it). It passes through the twelve zodiac constellations, and it is the pathway along which the Sun, Moon and planets appear to move. The zodiac is invisible and its position can only be detected by observing the position of the planets at night time.
When the ancient astronomer-priests studied the sky at night they noted that the five known planets, Mercury, Venus, Mars, Jupiter and Saturn moved about in repeating patterns on their orbital paths, but always within the same eighteen degree band of sky. It appeared that most of the movement in the night sky took place within this narrow band. Astronomers and astrologers focused their attention on it and studied any other movement within it. Sharing the band were twelve constellations known from ancient times as Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.
It is uncertain when the ancient Greeks first noted a correlation between the character of a person and the season of birth. It was probably in the third and second centuries BC. However, the ancient Greeks identified twelve characters and related them to the twelve signs of the zodiac (which in Greek, means “circle of animals”) but the circle did not have a beginning, they had to invent one. They decided the best way to begin the zodiac would be to begin at the vernal point where the two great circles, the ecliptic and the celestial equator intersect and the Sun crosses the vernal equinox at 0 degrees Aries. When they made their decision, the constellation Aries formed the background of fixed stars for the Sun as it crossed the vernal equinox at 0 degrees Aries (the spring equinox in the Northern Hemisphere) and the constellation name Aries was taken and fixed as the first sign of the tropical zodiac, followed by the other signs of the zodiac as we know them today.
The following old rhyme shows the order of the zodiac signs beginning with Aries the Ram which occurs on, or around twenty-first March each year.
The Ram, the Bull, the Heavenly Twins,
And next the Crab, the Lion shines,
The Virgin and the Scales,
The Scorpion, Archer and the Goat,
The Man who bears the Watering Pot,
And the Fish with glittering tails.