The zodiac is an area of the sky that extends approximately 8° north or south (as measured in celestial

latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the
year. The paths of the Moon and visible planets are also within the belt of the zodiac. [1]

The Earth in its orbit around the Sun causes the Sun to appear on the celestial sphere moving along the
ecliptic (red), which is tilted 23.44° with respect to the celestial equator (blue-white).

In Western astrology, and formerly astronomy, the zodiac is divided into twelve signs, each occupying
30° of celestial longitude and roughly corresponding to the constellations: Aries, Taurus, Gemini, Cancer,
Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.[2][3]

These astrological signs form a celestial coordinate system, or even more specifically an ecliptic
coordinate system, which takes the ecliptic as the origin of latitude and the Sun's position at vernal
equinox as the origin of longitude.[4]

Contents

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NameEdit

The English word zodiac derives from zōdiacus, the Latinized form of the Ancient Greek zōidiakòs kýklos
(ζῳδιακός κύκλος), meaning "cycle or circle of little animals". Zōidion (ζῴδιον) is the diminutive of zōion
(ζῷον, "animal"). The name reflects the prominence of animals (and mythological hybrids) among the
twelve signs.

UsageEdit

Modern zodiac wheel showing the 12 signs used in horoscopic astrology

The zodiac was in use by the Roman era, based on concepts inherited by Hellenistic astronomy from
Babylonian astronomy of the Chaldean period (mid-1st millennium BC), which, in turn, derived from an
earlier system of lists of stars along the ecliptic. [5] The construction of the zodiac is described in
Ptolemy's vast 2nd century AD work, the Almagest.[6]
Although the zodiac remains the basis of the ecliptic coordinate system in use in astronomy besides the
equatorial one,[7] the term and the names of the twelve signs are today mostly associated with
horoscopic astrology.[8] The term "zodiac" may also refer to the region of the celestial sphere
encompassing the paths of the planets corresponding to the band of about 8 arc degrees above and
below the ecliptic. The zodiac of a given planet is the band that contains the path of that particular body;
e.g., the "zodiac of the Moon" is the band of 5° above and below the ecliptic. By extension, the "zodiac
of the comets" may refer to the band encompassing most short-period comets.[9]

HistoryEdit

Further information: Former constellations

Early historyEdit

A 6th century mosaic zodiac wheel in a synagogue, incorporating Greek-Byzantine elements, Beit Alpha,
Israel

Zodiac circle with planets, c.1000 – NLW MS 735C

Further information: Babylonian star catalogues and MUL.APIN

The division of the ecliptic into the zodiacal signs originates in Babylonian astronomy during the first half
of the 1st millennium BC. The zodiac draws on stars in earlier Babylonian star catalogues, such as the
MUL.APIN catalogue, which was compiled around 1000 BC. Some constellations can be traced even
further back, to Bronze Age (First Babylonian dynasty) sources, including Gemini "The Twins," from
MAŠ.TAB.BA.GAL.GAL "The Great Twins," and Cancer "The Crab," from AL.LUL "The Crayfish," among
others.[citation needed]

Around the end of the 5th century BC, Babylonian astronomers divided the ecliptic into 12 equal "signs",
by analogy to 12 schematic months of 30 days each. Each sign contained 30° of celestial longitude, thus
creating the first known celestial coordinate system. According to calculations by modern astrophysics,
the zodiac was introduced between 409 and 398 BC and probably within a very few years of 401 BC. [10]
Unlike modern astrologers, who place the beginning of the sign of Aries at the place of the Sun at the
vernal equinox, Babylonian astronomers fixed the zodiac in relation to stars, placing the beginning of
Cancer at the "Rear Twin Star" (β Geminorum) and the beginning of Aquarius at the "Rear Star of the
Goat-Fish" (δ Capricorni).[11]

Due to the precession of the equinoxes, the time of year the Sun is in a given constellation has changed
since Babylonian times, the point of vernal equinox has moved from Aries into Pisces.[12]

Because the division was made into equal arcs, 30° each, they constituted an ideal system of reference
for making predictions about a planet's longitude. However, Babylonian techniques of observational
measurements were in a rudimentary stage of evolution. [13] They measured the position of a planet in
reference to a set of "normal stars" close to the ecliptic (±9° of latitude) as observational reference
points to help positioning a planet within this ecliptic coordinate system. [14]

In Babylonian astronomical diaries, a planet position was generally given with respect to a zodiacal sign
alone, less often in specific degrees within a sign. [15] When the degrees of longitude were given, they
were expressed with reference to the 30° of the zodiacal sign, i.e., not with a reference to the
continuous 360° ecliptic.[15] In astronomical ephemerides, the positions of significant astronomical
phenomena were computed in sexagesimal fractions of a degree (equivalent to minutes and seconds of
arc).[16] For daily ephemerides, the daily positions of a planet were not as important as the astrologically
significant dates when the planet crossed from one zodiacal sign to the next. [15]

Hebrew astronomy and astrologyEdit

Knowledge of the Babylonian zodiac is also reflected in the Hebrew Bible; E. W. Bullinger interpreted the
creatures appearing in the book of Ezekiel as the middle signs of the four quarters of the Zodiac, [17][18]
with the Lion as Leo, the Bull is Taurus, the Man representing Aquarius and the Eagle representing
Scorpio.[19] Some authors have linked the twelve tribes of Israel with the same signs or the lunar Hebrew
calendar having twelve lunar months in a lunar year. Martin and others have argued that the
arrangement of the tribes around the Tabernacle (reported in the Book of Numbers) corresponded to
the order of the Zodiac, with Judah, Reuben, Ephraim, and Dan representing the middle signs of Leo,
Aquarius, Taurus, and Scorpio, respectively. Such connections were taken up by Thomas Mann, who in
his novel Joseph and His Brothers attributes characteristics of a sign of the zodiac to each tribe in his
rendition of the Blessing of Jacob.[citation needed]

Hellenistic and Roman eraEdit

The 1st century BC Dendera zodiac (19th-century engraving)

The Babylonian star catalogs entered Greek astronomy in the 4th century BC, via Eudoxus of Cnidus.[20][21]
Babylonia or Chaldea in the Hellenistic world came to be so identified with astrology that "Chaldean
wisdom" became among Greeks and Romans the synonym of divination through the planets and stars.
Hellenistic astrology derived in part from Babylonian and Egyptian astrology.[22]Horoscopic astrology first
appeared in Ptolemaic Egypt (305 BC–30 BC). The Dendera zodiac, a relief dating to ca. 50 BC, is the first
known depiction of the classical zodiac of twelve signs.

The earliest extant Greek text using the Babylonian division of the zodiac into 12 signs of 30 equal
degrees each is the Anaphoricus of Hypsicles of Alexandria (fl. 190 BC).[23] Particularly important in the
development of Western horoscopic astrology was the astrologer and astronomer Ptolemy, whose work
Tetrabiblos laid the basis of the Western astrological tradition.[24] 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. [25] Ptolemy lived in the 2nd century AD, three centuries
after the discovery of the precession of the equinoxes by Hipparchus around 130 BC. Hipparchus's lost
work on precession never circulated very widely until it was brought to prominence by Ptolemy, [26] and
there are few explanations of precession outside the work of Ptolemy until late Antiquity, by which time
Ptolemy's influence was widely established. [27] Ptolemy clearly explained the theoretical basis of the
western zodiac as being a tropical coordinate system, by which the zodiac is aligned to the equinoxes
and solstices, rather than the visible constellations that bear the same names as the zodiac signs. [28]

Hindu zodiacEdi