12 Agt 2007

Zodiac (disambiguation).


The term zodiac denotes an annual cycle of twelve stations along the ecliptic, the apparent path of the sun across the heavens through the constellations that divide the ecliptic into twelve equal zones of celestial longitude.
The zodiac is the first known celestial coordinate system. There are two apparently independently created zodiacs. Babylonian astrology, inherited by Hellenistic and Indian astrology, developed the zodiac of twelve signs familiar in the West. In Chinese astrology, months and years pass through a cycle of twelve animals that imply certain fortunes or misfortunes related to events occurring within those signs. The Chinese zodiac is not linked to constellations, however.

The etymology of the term zodiac comes from the Latin zodiacus, from the Greek ζῳδιακός [κύκλος], meaning "[circle] of animals", derived from ζῴδιον, the diminutive of ζῷον "animal". However, the classical Greek zodiac also includes signs (also constellations) that are not represented by animals (e.g., Libra, Virgo, Gemini). Another suggested etymology is that the Greek term is cognate with the Sanskrit sodi, denoting "a path", i.e., the path through which the Sun travels.

The zodiac is also understood as a region of the celestial sphere that includes a band of eight arc degrees above and below the ecliptic, and therefore encompasses the paths of the Moon and the naked eye planets (Mercury, Venus, Mars, Jupiter, and Saturn). The classical astronomers called these planets wandering stars to differentiate them from the fixed stars of the celestial sphere (Ptolemy). Astrologers understood the movement of the planets and the Sun through the zodiac as a method to explain and predict events on Earth.

By 2,000 BC, the Egyptians and Mesopotamians marked the seasons by the constellations we now call Taurus, Leo, Scorpio, and Aquarius. However, the marking of seasons by constellations may go back to 5,000 BC. The division of the ecliptic into the zodiacal signs originates perhaps in Babylonian ("Chaldean") astronomy as early as the 1st millennium BC (likely during Median/"Neo-Babylonian" times) (Powell 2004).

The Babylonian calendar assigns each month a constellation, beginning with the position of the Sun at vernal equinox. Babylonian astronomers at some point during the 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).

Zodiacal constellations

The precise origins of the twelve constellations of the zodiac are unknown. In particular the reasons for the prominence given to animals is unclear (it is in fact a feature of all the constellations, not just those of the zodiac). The shape of the constellations themselves were probably not the main factor, as most of them bear little or no resemblance to the mythical characters after which they are named. Their origins are more likely to be in the belief of early peoples that events on earth were mirrored in the heavens above them. It followed then, that important mythical beings in the earth's affairs must have a matching image in the sky. Therefore over time a process probably developed whereby various important archetypal characters in ancient myth were linked to the sky by the 'discovery' of a pattern of stars (or 'constellation') in their image.

Because of their important location, the stars along the path of the ecliptic would have been given particular attention, and the constellations there ascribed to especially significant mythical beings or symbols. As the concept of the zodiac developed, these constellations gave their names to the celestial zones they inhabitated, and so by extension to the zodiac signs.
The original Babylonian zodiac consisted of eighteen signs ; however the twelve sign zodiac developed later on to become the permanent form, probably as twelve was the number of months in the Babylonian year. The present day names of the Western constellations and signs of the zodiac were first described by the Greek astronomer and astrologer Ptolemy who lived between 120 - 180 AD. The following are the twelve constellations with their Latin names which gave their names to the zodiac signs , which are still used by astronomers today

Zodiac in astrology

Astrologers use astronomical observations of the movements of the night sky for divinatory purposes. The zodiac remains in use in modern astrology, though the issue of tropical astrology (used mainly by Western astrologers) and sidereal astrology (used mainly by Indian astrologers) is central. At issue in the debate is whether the signs should be defined in terms of zones derived from nodal points defined by Earth's motion during a tropical year , or whether the signs should be defined in terms of signs roughly aligned with the constellations of the same name (for sidereal astrologers). This matters because of an astronomical phenomenon called the precession of the equinoxes, whereby the position of the stars in sky has changed over time. Therefore, over the centuries the twelve zodiacal signs in Western astrology no longer correspond to the same part of the sky as their original constellations, or their Indian counterparts. In effect, in Western astrology the link between sign and constellation has been broken, whereas in Indian astrology it remains of paramount importance.

Regardless of whether the tropical or sidereal definition of the zodiac is chosen, astrologers chart the positions of the sun and planets in relation to the zodiacal signs. The horoscope is used to associate properties of a sign with the properties of planets positioned in that sign. The planet is said to influence events on Earth but the way in which it does this is modified by the influence of the sign in which it is positioned.

The Western zodiac
The modern western astrological signs are simplifications of conventional pictorial representations of the signs, used since Hellenistic times. The characters are encoded in unicode at positions U+2648 to U+2653 (hexadecimal numbers).The glyph representation of these characters will depend on the font in which they are displayed.

Below are the Roman names of the signs of the zodiac (with the ecliptic longitudes of their first points). These figures represent the equivalent J2000.0 ecliptic longitudes for the sidereal zodiac described here in this article. The figures also represent ecliptic longitudes for a tropical zodiac where 0° Aries is understood as the vernal equinox:

Aries (0°) (The Ram)

Taurus (30°) (The Bull)

Gemini (60°) (The Twins)

Cancer (90°) (The Crab)

Leo (120°) (The Lion)

Virgo (150°) (The Virgin)

Libra (180°) (The Scales)

Scorpio (210°) (The Scorpion)

Sagittarius (240°) (The Archer)

Capricorn (270°) (The Sea-goat)

Aquarius (300°) (The Water Carrier)

Pisces (330°) (The Fishes)

The Indian Zodiac

Traditional Hindu astrology has a sidereal coordinate zodiac system with twelve signs. The names of the Hindu zodiacal signs, or rāśis, are similar to Graeco-Babylonian signs, apparently as a result of Indo-Greek contact:

1. meṣa "ram" (Aries)
2. vṛṣabha "bull" (Taurus)
3. mithuna "a pair" (Gemini)
4. karka "crab" (Cancer)
5. siṃha "lion" (Leo)
6. kanyā "girl" (Virgo)
7. tula, from tulā "balance" (Libra)
8. vrushchik "scorpion" (Scorpius), also kaurpi, loaned from the Greek
9. kārmuka, cāpa, dhanus "bow, arc", cāpin "armed with a bow" (Sagittarius)
10. eṇa, mṛga "antelope", also makara "sea-monster" (Capricornus)
11. kumbha "pitcher, water-pot" (Aquarius)
12. matsya "fish", also jhaṣa, timi, mīna after specific kinds of fish (Pisces)

This "Hindu zodiac" (adhvan, rāśi) thus has similarities to Greek zodiac. The Graeco-Babylonian system of twelve signs overlays the native Hindu system of nine grahas or planets.

Chinese and other zodiacs

Chinese astrology also has a system of twelve signs sometimes also referred to as "zodiac". This does not necessarily imply a common origin, since the number of twelve naturally suggests itself from the number of synodic months in a year; in other words, the extent of a zodiacal sign corresponds to the path covered by the Sun between two new moons. It is interesting to note, that despite the lack of a common origin, the Chinese zodiac also consists of animals. However, the Chinese zodiac associates each animal with both one month and one solar year. Thus the signs repeat themselves every twelve year cycle. The animals of the Chinese Zodiac are: rat, ox, tiger, rabbit (or hare), dragon, snake, horse, sheep (or goat), monkey, rooster (or phoenix), dog and pig (or boar). For a list of how these animals map to the months and years see Chinese astrology. There is also a Chinese lunar zodiac comprised of twenty-eight lunar "mansions", each corresponding to a Chinese constellation.

Beyond the traditional Chinese system, in New Age or Occultist movements there are sometimes claims of even other systems such as a "Celtic zodiac" based on the lunisolar Celtic calendar, or a "Galactic zodiac".Other evidence suggests Mayan, Incan and Aztec cultures of the Western hemisphere also noted celestial events along the zodiac. The Maya for example, certainly possessed a zodiac of some kind. The Mayan name for the constellation Scorpio was also 'scorpion', while the name of the constellation Gemini was 'peccary'. There is evidence for other constellations being named after various beasts, but it remains unclear.

Zodiac in astronomy

In astronomy the zodiacal constellations are a convenient way of marking the ecliptic (the sun's path across the sky). The zodiac is also a way for astronomers to mark the path of the moon and planets , as their movements also remain within these constellations. Apart from this role, the zodiacal constellations have no extra significance to astronomers than any other constellation.

Unlike the zodiac signs in astrology, which are all thirty degrees in length, the astronomical constellations vary widely in size. The boundaries of all the constellations in the sky were set by the International Astronomical Union (IAU) in 1930. This was essentially a mapping exercise to make the work of astronomers more efficient, and the boundaries of the constellations are not therfore in any meaningful sense an 'equivalent' to the zodiac signs. Along with the twelve original constellations, the boundaries of a thirteenth constellation, Ophiuchus, were set by astronomers within the bounds of the zodiac.

Comparison to modern systems

Though perhaps as old as 5,000 years, the zodiac coordinate system boasts advantages over its more common modern counterparts. Since the coordinate system is celestially centered, it is insulated from the many eccentricities of Earth's motion: including its rotation, intricacies of Earth time, precession, nutation and its elliptical and perturbed orbit around our Sun. To use the zodiac coordinate system all one has to know is where to find one of the nodal constellations that include the fixed reference points for the system: Taurus and Scorpio. Since those constellations are located on opposite sides of the ecliptic along the zodiac, one should always be visible in the night sky. Also. these constellations are both located within the prominent band of cloud and dust of the Milky Way. From these constellations astronomers can orient themselves for locating any point in the coordinate system.

The modern, commonly used tropical systems require an observer to know the current mean sidereal time, the observer's terrestrial longitude and latitude, and the epoch the observer wishes to utilize, and to account for other peculiarities of Earth's motion. Of course, modern astronomical computers handle most of the tasks for observers, but it involves a large effort by many different astronomers behind the scenes.

In addition, much of the motion of the stars in modern tropical coordinate systems can be attributed wholly to these peculiarities of Earth's motion. Astronomers make the distinction between the proper motion of a star (typically relatively subtle), from the other motion that arises totally from the designation of a tropical rather than sidereal coordinate system. One example where this exhibits itself is in the constellation boundaries drawn up by the IAU. The neat constellation boundaries drawn in 1930 exhibit increasingly distorted boundary lines over time. This may seem like something of little consequence, but why bother drawing neat boundaries around constellations if they inherently become erratic in the dominant coordinate system in use then and now.

Finally, since the zodiac system uses the ecliptic rather than the terrestrial equator for its equatorial plane it is not susceptible to the drifting of stars across the celestial equator as in the commonly used equatorial coordinate system (right ascension, declination). In The Almagest Ptolemy criticizes Hipparchus’ use of an equatorial plane in some of Hipparchus’ variously specified coordinate systems for this very reason (Ptolemy 1998).

These advantages make the zodiac coordinate system a very efficient system of coordinates in terms of requiring very little human-hours of labor to use and maintain: issues particularly important to early astronomers, typically working in often in isolation from one another.

The key disadvantage of a zodiac system of coordinates will manifest as a problem, if the nodal stars that serve as its fixed reference points for the system exhibit significant proper motion so that within the system of coordinates every other star appears to move dramatically in unison. In other words, selecting a star that has eccentiricities compared to the other stars undermines the usefulness of the system of coordinates. For example the inadvertent selection of an asteroid or an entire galaxy outside our Milky Way would lead to this condition. The reason for this is that celestial objects outside our galaxy revolve around our galaxy in a period of about 220 million years, at least in terms of a frame of reference affixed to our Sun and its neighboring stars. The only other sidereal coordinate system in common use today (that shares many of the zodiac’s advantages) is the galactic coordinate system. In galactic coordinates, the plane of the Milky Way and its own axial center serve as the fixed referents. These are fairly logical reference points for a coordinate system, though of course they cannot be located with the naked eye.

Another disadvantage relates to the apparatus required for orienting one to the coordinate system. Using geocentric coordinates astronomers can easily calibrate their instruments to the fixed reference point. As long as astronomers can obtain an accurate compass reading, they can orient themselves to a geocentric coordinate system (such as ecliptic or equatorial coordinates). Using zodiac coordinates requires an astronomer to locate the correct star, whether Antares or Aldebaran, and the correct constellation- Scorpio or Taurus respectively- and make an accurate reading of the position of that star and accurately orient that star to the ecliptic. This may take more skill than a mere compass reading: especially for amateur astronomers.

See Also
* History of astronomy
* History of astrology
* Astrological sign
* Chinese Zodiac
* Elements of the zodiac
* Babylonian influence on Greek astronomy
* Astronomical symbols
* Astrology and alchemy
* Esoteric cosmology
* Zodiacal constellation
* Zodiacal light
* Zodiacal dust
* Cusp (astrology)
* Sefer Raziel HaMalakh

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