Zodiac

From The Book of THoTH (Leaves of Wisdom)

The zodiac is an historical astronomical coordinate system based on the division of the ecliptic More precisely, the projection of the ecliptic onto the celestial sphere in a geocentric coordinate system into twelve equal "signs", each sign defining a specific ecliptic longitude of 30 degrees. Its principal use today is in astrology. It is centred on the apparent path of the Sun across the background stars called the ecliptic. The zodiac is usually also taken to include a band of about 8 degrees above and below the ecliptic, so that it comprises the paths of the Moon and the naked eye planets (Mercury, Venus, Mars, Jupiter, and Saturn).

The signs were historically used as the basis of ecliptic coordinates, so that any point on the celestial sphere could be associated with a sign of the zodiac by its normal projection onto the ecliptic.

1 List of signs
2 Historical origin
3 Sidereal zodiac
4 Other "zodiacs"
5 Astrology
6 Zodiacal Constellations
7 Notes
8 See also
9 External links

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List of signs

The signs were named after the nearby constellations at the time of Ptolemy, most of which were named after animals, hence the term zodiac (from Greek zodiakos [kyklos], "circle of little animals", from zodiaion, the diminutive of zoon "animal").

As defined by Claudius Ptolemy, each sign covers 30° of the ecliptic, beginning with the vernal equinox point which was then in the constellation of Aries. The vernal equinox remains the origin of the astronomical coordinate system even today, a fact which forces astronomers to work with epochs, currently usually fixed at J2000.0.

As of 2000, the vernal equinox is in the Pisces constellation, near the projection of the NGC 7787 spiral galaxy on the celestial sphere but continues to move because of precession of the equinoxes.

♈ Aries 0° (vernal equinox)
♉ Taurus 30°
♊ Gemini 60°
♋ Cancer 90° (summer solstice)
♌ Leo 120°
♍ Virgo 150°
♎ Libra 180° (autumnal equinox)
♏ Scorpius 210°
♐ Sagittarius 240°
♑ Capricornus 270° (winter solstice)
♒ Aquarius 300°
♓ Pisces 330°

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.

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Historical origin

The division of the ecliptic into the zodiacal signs originates in Babylonian ("Chaldean") astronomy in the early to mid 1st millennium BC (likely during Median/"Neo-Babylonian" times).The vernal equinox point lay near the beginning of the constellation of Aries around roughly 500 BC The system underwent modifications in Greek astronomy of Hellenism. The current definition of the zodiac was laid down by Ptolemy in the 2nd century, who used them as the basis of the celestial coordinate system used in his Almagest. Astrological meanings attached to the signs are inspired by the Hellenistic infatuation with Egyptian mythology.

The zodiacal signs remained in use as the basis of an ecliptic coordinate system throughout the Middle Ages, replaced by equatorial coordinate systems in Early Modern times. Thus, Hermannus Contractus in his de mensura astrolabii liber gives the locations of stars in stereographic projection for the construction of an astrolabe, for example giving the ecliptic coordinate of Altair (Altahir vel Abiatra) as 14. Scorpius, equalling an ecliptic longitude of 223° (the 14th degree from the beginning of Scorpius at 210°).

The zodiacal symbols are Early Modern simplifications of conventional pictorial representations of the signs, attested since Hellenistic times. The symbols are encoded in Unicode at positions U+2648 to U+2653.

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Sidereal zodiac

For naked eye observations, the difference between sidereal and tropical coordinate systems becomes only relevant diachronically, over the course of several centuries. Since the precession of the equinoxes was discovered by Hipparchus around 130 BC, the point could not have been a matter of debate before that date.

Traditional Hindu astrology knows a related coordinate system with twelve signs. The names of the Hindu zodiacal signs, or {{{3|IAST}}}s, are clearly derived from the Graeco-Babylonian signs, apparently the result of Indo-Greek contact:

ram (Aries)
bull (Taurus)
a pair(Gemini)
crab (Cancer)
lion (Leo)
girl (Virgo)
balance (Libra)
scorpion (Scorpius), also kaurpi, loaned from the Greek
bow, arc, armed with a bow (Sagittarius)
antelope, also sea-monster (Capricornus)
pitcher, water-pot (Aquarius)
fish, also after specific kinds of fish (Pisces)

The Hindu zodiac is thus a direct descendant of the Greek zodiac. The Graeco-Babylonian system of twelve signs overlays the native Hindu system of nine grahas or houses. The difference between the Hindu {{{3|IAST}}}s and the Western zodiacal signs is due to the sidereal system used by the Hindus, linking the signs to constellations rather than the course of the Sun. This difference increases by approximately one degree every 70 years, and is currently of the order of 24 degrees, corresponding to a separation of 1700 years, consistent with Indo-Greek transmission in the first centuries AD.

The term sidereal zodiac may refer both to the Hindu system, and to recent attempts in western astrology to tie the zodiac signs to their "original" locations relative to the background stars. The zodiac of Greek astronomy is referred to as tropical zodiac in this context, a retronym disambiguating it from the sidereal zodiac.

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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.

Beyond the traditional Chinese system, In New Age or Occultist movements there are sometimes claims of even other systems such as a "Celtic zodiac"[1] [2] based on the lunisolar Celtic calendar, or a "Galactic zodiac" [3]

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Astrology

Astrologers would use astronomical observations of the movements of the night sky for divinatory purposes. The zodiac remains in use in western tropical astrology, associating various qualities with the individual signs, in particular with the astrological birth sign, the zodiacal sign comprising the position of the Sun at the moment of a person's birth, associating mythical properties of a sign with character traits. 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 a 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.

Tropical astromony is in opposition to sidereal astrology, where over the centuries, the signs do not shift with respect to the background stars but rather with respect to the seasons of the year. An example of such a system is Hindu astrology, and in the 20th century, there have also been movements in western astrology towards a sidereal zodiac.

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Zodiacal Constellations

The signs of the zodiac are not to be confused with the actual constellations for which they are named. Because of the precession of the equinoxes, the zodiacal signs have shifted away from their constellations, so that today, the beginning of the sign of Aries, defined as the position of the Sun on vernal equinox, lies somewhere within the constellation Pisces.

Moreover, the ecliptic passes a thirteenth constellation, Ophiuchus, but this constellation is not considered part of the zodiac. The constellation of Ophiuchus was recognised as a zodiacal constellation in Ptolemy's Almagest. 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.

The following table compares the Gregorian dates on which the sun enters

a sign in the Ptolemaic tropical zodiac
a sign in the sidereal system of Cyril Fagan, introduced in 1944
the astronomical constellation by the same name, with constellation boundaries as defined in 1930 by the International Astronomical Union.

The dates can vary by as much as 2 days from year to year, depending on the cycle of leap years.

Sign	Symbol	Astrological Dates		Astronomical Dates (as of AD 1977)	Elements of the zodiac
Sign	Symbol	Tropical zodiac	Sidereal zodiac	Astronomical Dates (as of AD 1977)	Elements of the zodiac
Aries	ram	March 21 – April 19	April 14 – May 14	April 19 – May 14	Fire
Taurus	Bull	April 20 – May 20	May 15 – June 14	May 14 – June 21	Earth
Gemini	twins	May 21 – June 20	June 15 – July 16	June 21 – July 21	Air
Cancer	crab	June 21 – July 22	July 17 – August 16	July 21 – August 11	Water
Leo	lion	July 23 – August 23	August 17 – September 16	August 11 – September 17	Fire
Virgo	virgin	August 24 – September 23	September 17 – October 17	September 17 – October 31	Earth
Libra	scale	September 24 – October 22	October 18 – November 16	October 31 – November 23	Air
Scorpio	scorpion	October 23 – November 21	November 17 – December 15	November 23 – November 30	Water
Sagittarius	archer	November 22 – December 21	December 16 – January 14	December 18 – January 19	Fire
Capricornus	seagoat	December 22 – January 19	January 15 – February 12	January 19 – February 16	Earth
Aquarius	water bearer	January 20 – February 18	February 13 – March 14	February 16 – March 12	Air
Pisces	fish	February 19 – March 20	March 15 – April 13	March 12 – April 19	Water