The Zodiac in Modern and Ancient Astrology

The 'Zodiac' denotes an annual cycle of twelve stations or "signs" along the ecliptic, the apparent path of the Sun across the heavens, dividing the ecliptic into twelve equal zones of celestial longitude. As such, the zodiac is a celestial coordinate system, more precisely an ecliptic coordinate system, taking the ecliptic as the origin of latitude, and the position of the sun at vernal equinox as the origin of longitude.

The Three Qualities

The Qualities assign the Signs into Quadruplicities, three groups of four. They are occasionally referred to as crosses because each quality forms a cross when drawn across the zodiac. Christian astrology relates the three qualities to the three aspects of God in the trinity.

Cardinal signs (Aries, Cancer, Libra and Capricorn) are associated with initiation and creativity.
Fixed signs (Taurus, Leo, Scorpio and Aquarius) are associated with stabilization and determination.
Mutable signs (Gemini, Virgo, Sagittarius and Pisces) are associated with resourcefulness, holism and adaptability.

Astronomy and The Constellations

Astronomically speaking (as opposed to astrologically) the zodiac may refer to the region of the celestial sphere encompassing the paths of the Moon and the naked eye planets (Mercury, Venus, Mars, Jupiter, and Saturn), corresponding to the band of about eight arc degrees above and below the ecliptic. The zodiac of a given planet is the band which contains the path of that particular body, e.g. the "zodiac of the Moon" is the band of five degrees above and below the ecliptic. By extension, the "zodiac of the comets" may refer to the band encompassing most short-period comets.

History

The division of the ecliptic into the zodiacal signs originates in Babylonian ("Chaldean") astronomy during the first half of the 1st millennium BC, likely during Median/"Neo-Babylonian" times (7th century BC), continuing earlier (Bronze Age) systems of lists of stars. Babylonian astronomers at some point during the early 1st millennium BC divided the ecliptic into twelve equal zones of celestial longitude to create the first known celestial coordinate system: a coordinate system that boasts some advantages over modern systems (such as equatorial coordinate system or ecliptic coordinate system).

The Babylonian calendar as it stood in the 7th century BC assigns each month a constellation, beginning with the position of the Sun at vernal equinox, which at the time was the Aries constellation ("Age of Aries"), for which reason first astrological sign is still called "Aries" even after vernal equinox has moved away from the Aries constellation.

The Babylonian zodiac also finds reflection in the Hebrew Bible. The name of the twelve signs are equivalent to the names in use today, except that the name of the Eagle seems to have been usually substituted for Scorpio. The arrangement of the twelve tribes of Israel around the Tabernacle (Numbers 2) corresponded to the order of the Zodiac; and four of the tribes represented the middle signs of each quarter: Judah was the Lion, Reuben the Man, Ephraim the Bull, and Dan the Eagle. The faces of the cherubim, in both Ezekiel and Revelation, are the middle signs of the four quarters of the Zodiac: the Lion is Leo; the Bull is Taurus; the Man is Aquarius; and the Eagle is Scorpio.

Particularly important in the development of horoscopic astrology was the astrologer and astronomer Ptolemy, whose work, the Tetrabiblos laid the basis of the Western astrological tradition. Under the Greeks and Ptolemy in particular, the planets, Houses, and signs of the zodiac were rationalized and their function set down in a way that has changed little to the present day. Ptolemy lived in the 2nd century AD, three centuries after the discovery of the precession of the equinoxes by Hipparchus around 130 BC, but he ignored the problem, apparently by dropping the concept of a fixed celestial sphere and adopting what is referred to as a tropical coordinate system instead.