Zodiac

See also: Zodiac (disambiguation)

Wheel of the zodiac: This 6th century mosaic pavement in a synagogue incorporates Greek-Byzantine elements, Beit Alpha, Israel.

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

In astronomy , the zodiac (Greek: ζῳδιακός, zōdiakos) is the ring of constellations that lines the ecliptic, which is the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon and planets also lie roughly within the ecliptic, and so are also within the constellations of the zodiac. In astrology, the zodiac denotes those signs that divide the ecliptic into twelve equal zones of celestial longitude. As such, the zodiac is a celestial coordinate system, or more specifically 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.

It is known to have been 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. The construction of the zodiac is described in Ptolemy's Almagest (2nd century AD).

The term zodiac derives from Latin zōdiacus, which in its turn comes from the Greek ζῳδιακὸς κύκλος (zōdiakos kuklos), meaning "circle of animals", derived from ζώδιον (zōdion), the diminutive of ζῶον (zōon) "animal". The name is motivated by the fact that half of the signs of the classical Greek zodiac are represented as animals (besides two mythological hybrids).

Although the zodiac remains the basis of the ecliptic coordinate system in use in astronomy besides the equatorial one, the term and the names of the twelve signs are today mostly associated with horoscopic astrology.

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 eight 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 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==twelve tribes of Israel with the twelve signs. 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.

Hellenistic and Roman era

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

The Babylonian star catalogues entered Greek astronomy in the 4th century BC, via Eudoxus of Cnidus and others. 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 syncretically originated from Babylonian and Egyptian astrology. Horoscopic astrology first appeared in Ptolemaic Egypt. The Dendera zodiac, a relief dating to ca. 50 BC, is the first known depiction of the classical zodiac of twelve signs.

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. Under theday. 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, by dropping the concept of a fixed celestial sphere and adopting what is referred to as a tropical coordinate system instead.

Hindu zodiac

The Hindu zodiac is believed to be adopted from the Greek system, during the period of intense Indo-Greek cultural contact during the Seleucid period (2nd to 1st centuries BC), but the two are not identical. The Hindu system uses sidereal coordinate system referenced to the fixed stars, but the Tropical system followed by the Greeks is referenced to the seasons in the Northern hemisphere. The latter is affected by the precession of the equinoxes. As a result, the European and the Hindu zodiacs were aligned at the time of Indo-Greek cultural contact but have gradually moved apart over two millennia that have passed since.

The Hindu zodiac signs and corresponding Greek signs sound very different, being in Sanskrit and Greek respectively, but their symbols are nearly identical. For example, dhanu means "bow" and corresponds to Sagittarius, the "archer", and kumbha means "water-pitcher" and corresponds to Aquarius, the "water-carrier". The correspondence of signs is taken to mean that Sanskrit names were translated from Greek names, and not the other way around.

Middle Ages and Early Modern period

The zodiac signs as shown in a 16th-century woodcut

A 17th-century fresco from the Cathedral of Living Pillar in Georgia depicting Christ within the Zodiac circle

The High Middle Ages saw a revival of Greco-Roman magic, first in Kabbalism and later continued in Renaissance magic. This included magical uses of the zodiac, as found, e.g., in the Sefer Raziel HaMalakh.

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 n the Miscellaneous Symbols block...

The twelve signs

Main article: Astrological sign

What follows is a list of the twelve signs of the modern zodiac (with the ecliptic longitudes of their first points), where 0° Aries is understood as the vernal equinox, with their Latin, Greek, Sanskrit, and Babylonian names (but note that the Sanskrit and the Babylonian name equivalents denote the constellations only, not the tropical zodiac signs). Also, the "English translation" is not usually used by English speakers. The Latin names are standard English usage.

№	Symbol	Long.	Latin name	English translation	Greek name	Sanskrit name	Sumero-Babylonian name
1	♈	0°	Aries	The Ram	Κριός/Kriós	Meṣa (मेष)	MUL LUḪUN.GA "The Agrarian Worker", Dumuzi
2	♉	30°	Taurus	The Bull	Ταῦρος/Tauros	Vṛiṣabha (वृषभ)	MULGU4.AN.NA "The Steer of Heaven"
3	♊	60°	Gemini	The Twins	Δίδυμοι/Didymoe	Mithuna (मिथुन)	MULMAŠ.TAB.BA.GAL.GAL "The Great Twins" (Lugalgirra and Meslamta-ea)
4	♋	90°	Cancer	The Crab	Καρκῖνος/Karkinos	Karkaṭa (कर्कट)	MULAL.LUL "The Crayfish"
5	♌	120°	Leo	The Lion	Λέων/Léōn	Siṃha (सिंह)	MULUR.GU.LA "The Lion"
6	♍	150°	Virgo	The Maiden	Παρθένος/Parthénos	Kanyā (कन्या)	MULAB.SIN "The Furrow"; "The Furrow, the goddess Shala's ear of corn"
7	♎	180°	Libra	The Scales	Ζυγός/Zygós	Tula (तुला)	zibanitum "The Scales"
8	♏	210°	Scorpio	The Scorpion	Σκoρπιός/Skorpiós	Vṛścika (वृश्चिक)	MULGIR.TAB "The Scorpion"
9	♐	240°	Sagittarius	Centaur The Archer	Τοξότης/Toxótēs	Dhanus (धनुष)	MULPA.BIL.SAG, Nedu "soldier"
10	♑	270°	Capricorn	"Goat-horned" (The Sea-Goat)	Αἰγόκερως/Aegókerōs	Makara (मकर)	MULSUḪUR.MAŠ "The Goat-Fish"
11	♒	300°	Aquarius	The Water Bearer	Ὑδροχόος/Hydrokhóos	Kumbha (कुम्भ)	MULGU.LA "The Great One", later qâ "pitcher"
12	♓	330°	Pisces	The Fish	Ἰχθύες/Ιkhthyes	Mīna (मीन)	MULSIM.MAḪ "The Tail of the Swallow", later DU.NU.NU "fish-cord"

The symbols used in Western astrology to represent the astrological signs

Zodiacal constellations

It is important to distinguish the zodiacal signs from the constellations associated with them, not only because of their drifting apart due to the precession of equinoxes but also because the physical constellations by nature of their varying shapes and forms take up varying widths of the ecliptic. Thus, Virgo takes up fully five times as much ecliptic longitude as Scorpius. The zodiacal signs, on the other hand, are an abstraction from the physical constellations designed to represent exactly one twelfth of the full circle each, or the longitude traversed by the Sun in about 30.4 days.

There have always been a number of "parazodiacal" constellations that are also touched by the paths of the planets. The MUL.APIN lists Orion, Perseus, Auriga and Andromeda. Furthermore, there are a number of constellations mythologically associated with the zodiacal ones: Piscis Austrinus, The Southern Fish, is attached to Aquarius. In classical maps, it swallows the stream poured out of Aquarius' pitcher, but perhaps it formerly just swam in it. Aquila, The Eagle, was possibly associated with the zodiac by virtue of its main star, Altair. Hydra in the Early Bronze Age marked the celestial equator and was associated with Leo, which is shown standing on the serpent on the Dendera zodiac. Corvus is the Crow or Raven mysteriously perched on the tail of Hydra. The MUL.APIN glosses Hydra as "the Snake Ningizzida, lord of the Netherworld". Ningizzida together with Dumuzi (Aries) and Pabilsag (Sagittarius) governed the household of the queen of the underworld.

Taking the current constellation boundaries as defined in 1930 by the International Astronomical Union, the ecliptic itself passes through an additional thirteenth constellation, Ophiuchus, situated between Scorpius and Sagittarius. This was identified in Ptolemy's Almagest, but is not generally recognised as part of the Zodiac. The idea of introducing Ophiuchus as a sign of the zodiac dates to the 1970s and was popularized in Japanese sidereal astrology from the late 1990s by Walter Berg's The 13 Signs of the Zodiac.

Table of dates

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

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

The theoretical beginning of Aries is the moment of vernal equinox, and all other dates shift accordingly. The precise Gregorian times and dates vary slightly from year to year as the Gregorian calendar shifts relative to the tropical year. These variations remain within less than two days' difference in the recent past and the near-future, vernal equinox in UTC always falling either on 20 or 21 of March in the period of 1797 to 2043, falling on 19 March in 1796 the last time and in 2044 the next. In the long term, if the Gregorian calendar is not reformed, the equinox will move to earlier dates: it will fall on 18 March for the first time in AD 4092.

Sign				Constellation
Name	Symbol	Tropical zodiac (2011)	Sidereal zodiac (Jyotisha) (2024, UTC)	Name	IAU constellation boundaries (2024)	Solar stay	Brightest star
Aries		21 March – 19 April	14 April – 14 May	Aries	19 April – 13 May	25.5 days	Hamal
Taurus		20 April – 20 May	14 May – 14 June	Taurus	14 May – 19 June	38.2 days	Aldebaran
Gemini		21 May – 20 June	14 June – 14 July	Gemini	20 June – 20 July	29.3 days	Pollux
Cancer		21 June – 22 July	14 July – 14 August	Cancer	21 July – 9 August	21.1 days	Al Tarf
Leo		23 July – 22 August	14 August – 13 September	Leo	10 August – 15 September	36.9 days	Regulus
Virgo		23 August – 22 September	13 September – 14 October	Virgo	16 September – 30 October	44.5 days	Spica
Libra		23 September – 22 October	14 October – 13 November	Libra	31 October – 22 November	21.1 days	Zubeneschamali
Scorpio		23 October – 21 November	13 November – 14 December	Scorpius	23 November – 29 November	8.4 days	Antares
Sagittarius		22 November – 21 December	14 December – 13 January	Sagittarius	18 December – 18 January	33.6 days	Kaus Australis
Capricorn		22 December – 19 January	13 January – 12 February	Capricornus	19 January – 15 February	27.4 days	Deneb Algedi
Aquarius		20 January – 18 February	12 February – 14 March	Aquarius	16 February – 11 March	23.9 days	Sadalsuud
Pisces		19 February – 20 March	14 March – 14 April	Pisces	12 March – 18 April	37.7 days	Eta Piscium

Because the Earth's axis is at an angle, some signs take longer to rise than others, and the further away from the equator the observer is situated, the greater the difference. Thus, signs are spoken of as "long" or "short" ascension.

Precession of the equinoxes

Further information: Precession of the equinoxes, Epoch (astronomy), Sidereal astrology, Tropical astrology, Astrological age, and Ayanamsa

Path taken by the point of vernal equinox along the ecliptic over the past 6000 years

The zodiac system was developed in Babylonia, some 2,500 years ago, during the "Age of Aries". At the time, the precession of the equinoxes was unknown, and the system made no allowance for it. Contemporary use of the coordinate system is presented with the choice of interpreting the system either as sidereal, with the signs fixed to the stellar background, or as tropical, with the signs fixed to the point of vernal equinox.

Western astrology takes the tropical approach, whereas Hindu astrology takes the sidereal one. This results in the originally unified zodiacal coordinate system drifting apart gradually, with an angular velocity of about 1.4 degrees per century.

For the tropical zodiac used in Western astronomy and astrology, this means that the tropical sign of Aries currently lies somewhere within the constellation Pisces ("Age of Pisces").

The origin for the sidereal coordinate system is known as the ayanamsa, a Sanskrit word. It is unclear when Indians became aware of the precession of the equinoxes, but Bhaskar-ii in Siddhanta Shiromani gives equations for measurement of precession of equinoxes, and says his equations are based on some lost equations of Suryasiddhanta plus the equation of Munjaala.

It is not entirely clear how the Hellenistic astronomers responded to this phenomenon of precession once it had been discovered by Hipparchus around 130 BC. Today, some read Ptolemy as dropping the concept of a fixed celestial sphere and adopting what is referred to as a tropical coordinate system instead: in other words, one fixed to the Earth's seasonal cycle rather than the distant stars.

Some modern Western astrologers, such as Cyril Fagan, have advocated abandoning the tropical system in favour of a sidereal one.

In modern astronomy

Further information: Epoch (astronomy)

The zodiac is a spherical celestial coordinate system. It designates the ecliptic as its fundamental plane and the position of the Sun at Vernal equinox as its prime meridian.

In astronomy, the zodiacal constellations are a convenient way of marking the ecliptic (the Sun's path across the sky) and the path of the moon and planets along the ecliptic. Modern astronomy still uses tropical coordinates for predicting the positions the Sun, Moon, and planets, except longitude in the ecliptic coordinate system is numbered from 0° to 360°, not 0° to 30° within each sign. Longitude within individual signs was still being used as late as 1740 by Jacques Cassini in his Tables astronomiques.

Zodiac is also used to refer to the zodiacal cloud of dust grains that move among the planets and the zodiacal light that originates from their scattering of sunlight.

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, in essence, a mapping exercise to make the work of astronomers more efficient, and the boundaries of the constellations are not therefore in any meaningful sense an 'equivalent' to the zodiac signs.

Mnemonics for the zodiac

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.

A less poetic, but succinct and perhaps more memorable, mnemonic is the following:

The Ramble Twins Crab Liverish;

Scaly Scorpions Are Good Water Fish.

(Ram-Ble = Ram, Bull; Twins = Twins; Crab = Crab; Li-Ver(ish) = Lion, Virgin; Scaly = Scale; Scorpion = Scorpio; Are = Archer; Good = Goat; Water = Water Bearer; Fish = Fish)

Another easy mnemonic:

All The Great Constellations Live Very Long Since Stars Can't Alter Physics.

(Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces)

One more easy mnemonic:

As The Great Cook Likes Very Little Salt, She Compensates Adding Pepper.

(Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces)

Remembering the translations/shapes of constellations with a fun mnemonic:

Really Boring Teachers Can Live Very Sadly Since Apples Give Worthless Feelings.

(Ram, Bull, Twins, Crab, Lion, Virgin, Scales, Scorpion, Archer, Goat, Water Bearer, Fish)

All That Gold Can Load Very Lazy Students Since Children Are at Play

(Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces)

See also

• Astronomical symbols
• Circle of stars
• Cusp (astrology)
• Elements of the zodiac
• Alexander A. Gurshtein

References

• B. L. van der Waerden, "History of the zodiac", Archiv für Orientforschung 16 (1953) 216–230.
• Emelianov, Vladimir. Nippurskij kalendar' i rannjaja istorija Zodiaka (Nippur Calendar and the Early History of Zodiac). St.-Petersburg, Peterburgskoje vostokovedenje, 1999.
• Ptolemy, Claudius (1998). The Almagest. Princeton, New Jersey: Princeton University Press. ISBN 0691002606. Translated and annotated by G. J. Toomer; with a foreword by Owen Gingerich.
• Powell, Robert, Influence of Babylonian Astronomy on the Subsequent Defining of the Zodiac (2004), PhD thesis.
• Tropical v Sidereal debate, The Traditional Astrologer magazine, (Ascella), Issue 14, May 1997, pp. 23–27
• Peters, Christian Heinrich Friedrich and Edward Ball Knobel. Ptolemy's Catalogue of Stars: a revision of the Almagest. (1915). Publishers, Carnegie Institution of Washington.