This article is about the astrological concept. For other uses, see zodiac (disambiguation)

Historical origin

The origins of the zodiac lie in Sumer in Mesopotamia.

See the History of astrology article for a detailed discussion.

Astronomy

In astronomy, the zodiac is the region of the sky close to the circle on which the orbital plane of our solar system intersects the celestial sphere. It includes the apparent path of the sun across the sky, known as the ecliptic, and the apparent paths of the naked eye planets which move in a zone just above and below this. It is a useful region of the sky to define, because it has practical implications for observations from the earth's surface. A bright object lying outside of the zodiacal region cannot be a planet. Polar observatories cannot easily observe the planets, because the zodiac is too close to the horizon.

The zodiac is traditionally thought of as comprising a certain set of constellations. The constellations of both zodiacs are shown in the table below, including Ophiuchus, which was recognised as a zodiacal constellation at least as far back as Ptolemy's Almagest in the 2nd century.

Most of Ophiuchus is north of the ecliptic - however, there are a few stars of Ophiuchus which are south of the ecliptic. Ptolemy recognised 4 of them, which are today known as 36 Oph, 42 θ Oph, 44 Oph and 51 Oph, and he recognised that they were south of the path of the sun through the sky. Thus, although the 1930 decision by the International Astronomical Union to adopt constellation boundaries is a common reason given by astrologers for the inconsistency, Ophiuchus as a recognised zodiacal constellation predates this IAU decision by at least 1,700 years.

In modern astronomy, the zodiacal constellations, like all constellations, are recognized as chance visual groupings of stars, with no natural significance. In most cases they are not groupings of stars in three-dimensional space. In a few cases, parts of constellations are made up of stars that are close in space as well as in the sky. We see the sky without any perception of its depth; two stars that are neighbours in a constellation are usually three-dimensionally not close to each other. Star clusters and star systems are exceptions.

Astrology

In western astrology the zodiac is a band on the celestial sphere which contains the perceived paths of the Sun, Moon, and principal planets and is divided into twelve equal parts of 30° each, called "signs of the zodiac" or astrological signs, each named for a constellation. At the centre of this band is the plane of the ecliptic. The width of the zodiac allows for the fact that the orbits of the other bodies are inclined relative to plane of the ecliptic, and thus extend about 8º above and below the ecliptic.

In western tropical astrology, the zodiacal year begins at the point where the plane of the ecliptic intersects with the earth's equatorial plane at the vernal equinox. This is when the Sun moves into the northern hemisphere of the earth's equatorial plane. Thus the Sun always enters the astrological zodiacal sign of Aries at the vernal equinox about March 20, but it will not cross into the astronomical constellation of the same name until nearly a month later. So in western tropical astrology, although the signs derive their names from the constellations, they are not the same thing.

In sidereal astrology the zodiacal signs are aligned to their correct astronomical stellar constellations. The alignment still isn't precise, because the constellations all take up varying amounts of space along the ecliptic, whereas the zodiacal signs each take up exactly 30°.

Zodiacal Constellations

The zodiac includes twelve of the constellations that the ecliptic crosses. It actually crosses a thirteenth, Ophiuchus, but this constellation is not considered part of the zodiac (see above). Because the ecliptic lies in the general plane of the solar system, the Sun, Moon, and planets seem to move through the zodiacal constellations.

A traditional mnemonic:

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 holds the Watering Pot,

And Fish with glittering scales.

The following table compares the dates that the sun enters a sign in tropical (Ptolemaic) and sidereal (Vedic) astrological systems, and the date when it enters the astronomical constellation by the same name. The dates can vary by as much as 2 days, from year to year, depending on the cycle of leap years, and the precession of the perihelion of the Earth's orbit over many centuries.

The "tropical" zodiacal dates (those that divide the zodiac starting with the vernal equinox) are used primarily in the United States and western Europe. The "sidereal" dates (those that divide the zodiac starting with the alignment of the Sun with a distant star in Aries) are used primarily in India. Many people who don't know anything about constellations have heard about the signs of the Zodiac in an astrological context.

Astrologers would use astronomical observations of the movements of the night sky for divinatory purposes. Some of these applications were founded on correspondences between practical knowledge and celestial observations (for example, the relationship between solar position and stellar positions depends on the season, which has practical implications for agriculture), whilst others have no natural source.

The familiar "star sign", or more precisely the "sun sign", under which a person is born refers to the position of the sun in the signs on the tropical ecliptic at the time of his or her birth. Because of the precession of the equinoxes over the last three thousand years or so, the signs are out of phase with the astronomical constellations for which they are named by about a month. A few modern western astrologers, in common with those of India, cast horoscopes with reference to the actual constellations, rather than the signs. This is known as sidereal astrology.

The idea of an astrological birth sign is that the person would have some characteristics of the mythic symbolism that the ancients identified with that constellation; so, for example, a "Libra" (the scales) will be balanced and stable. Also, because the planets are all found in the zodiac, the position of the Moon or a planet in a particular sign would have an effect on the life of that person. For example: A person may be born on June 1st. This is near the center of the sign of Gemini, and so Gemini would be his sun sign. Any planets also observed near the center of Gemini, would be in "conjunction" with the sun, and said to have a particularly strong effect on the destiny and personality of the person. At the same time, other planets are in other signs of the zodiac, and their effects would be felt on the portions of a person's life "ruled" by that sign. Significance is also associated to the angular positions of planets and signs relative to each other at the moment of a birth or other significant event.

Angels of the zodiac

With the Christianization of Europe, angels were associated with the signs of the zodiac to replace the traditional gods. The traditional correlations are as follows:

The zodiac as a calendar

The concept of the zodiac was originated by the Babylonians certainly before 2000 BC as a method of visualizing the passage of time. The zodiac worked as a symbolic calendar. It was divided into twelve parts as suggested by the appearance of 12 moons in a year. The signs are geometric divisions of the celestial sphere, each corresponding to one twelfth of a year.

The signs of the zodiac, as enumerated by Egyptian astronomer, Ptolemy, in the 2nd-century AD, are the ones we know today. The same names are used for both signs in astrology and for constellations in astronomy, but it's important to make a distinction between signs and constellations. Signs are geometric sections, each 30В° wide, corresponding with particular periods of time of the year, but which don't necessarily physically correspond with the constellations of the same name.

By the time of Ptolemy the zodiac was already at least two thousand years old. But together with its burgeoning astrological use the basic function and structure of the "calendar of the zodiac" remained. The sign of Aries marks the beginning of the year at the vernal equinox. The retreating crab in Cancer represents the retreat of the Sun from its farthest northern point at the time of the summer solstice. Leo, the symbol of fire, represents summer heat. The scales of Libra signify the balance between day and night at the autumnal equinox. The decline of the sun's power is represented in Scorpio by the scorpion, the symbol of darkness. The water-bearer, Aquarius, represents the rainy season which, in Egypt, meant the yearly flooding of the Nile. The fishes of Pisces, symbolize the return of life and the resumption of agriculture.

The concept of the zodiac spread from Babylonia to Greece and, from there, to Egypt where the Egyptians substituted their own symbolism. Aries became the Fleece. Two Sprouting Plants replaced the twins of Gemini. Cancer was re-named Scarabaeus. Leo became the Knife and Libra the Mountain of the Sun. Sagittarius was reduced to just an arrow. Capricorn became the image of life, represented by a mirror. Scorpio became a serpent. Aquarius became simply water, while Taurus, Virgo and Pisces were not changed.

See also

• Astrological sign
• Angels of the zodiac
• Elements of the zodiac
• Astronomical symbols
• Chinese astrology
• Astrology and alchemy
• Esoteric cosmology
• Barren sign
• Zodiac stones are birthday gifts according to the recipient's zodiac sign

External links

• Chinese Zodiac Chart Find your Chinese Zodiac sign based on your date of birth.
• Celtic Zodiac — Folklore and history of the Celtic zodiac.
• Zodiacs — A site detailing the various zodiacs in depth.
• Ophiuchus — The problem of Ophiuchus - the so-called 13th sign of the Zodiac.
• A guide to free horoscopes with selected sites, lessons for beginners and horoscopes freeware.
• Born Under Ophiuchus and Ignored by the Horoscopes: A Modern Dilemma — An article discussing the omission of Ophiuchus from the Zodiac by astrologers.

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