Zodiac

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 on 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 sky over the course of the year. The Moon and planets also lie 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, to be more precise, 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.[1] The construction of the zodiac is described in Ptolemy's Almagest (2nd century AD). 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 [2]

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 as well as 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.

Contents

History

The 1st century BC Denderah zodiac (19th-century engraving)
Further information: Babylonian zodiac, History of astronomy, and History of astrology

The division of the ecliptic into the zodiacal signs originates in Babylonian ("Chaldean") astronomy during the first half of the 1st millennium BC, likely during Median/"Neo-Babylonian" times (7th century BC),[3] continuing earlier (Bronze Age) systems of lists of stars. Babylonian astronomers at some point during the early 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). The Babylonian calendar as it stood in the 7th century BC assigns each month a constellation, beginning with the position of the Sun at vernal equinox, which, at the time, was the Aries constellation ("Age of Aries"), for which reason the first astrological sign is still called "Aries" even after the vernal equinox has moved away from the Aries constellation due to the slow precession of the Earth's orbit around the Sun. A scientific analysis of the constellations suggests Aries' was located at the vernal equinox at the time of the Bronze Age (~2700 BC),[4][5] thereby suggesting an earlier establishment of the constellations.

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.

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

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.

Hindu astrology adopted the Hellenistic zodiac during the Seleucid period (2nd to 1st centuries BC), a period of intense Indo-Greek cultural contact. The transmission of the zodiac system to Hindu astrology predated widespread awareness of the precession of the equinoxes, and the Hindu system ended up using a sidereal coordinate system (as opposed to the Tropical System followed by the Greeks), which resulted in the European and the Hindu zodiacs, even though sharing the same origin in Hellenistic astrology, gradually moving apart over two millennia that have passed since. The Sanskrit names of the signs are direct translations of the Greek names (dhanus meaning "bow" rather than "archer", and kumbha meaning "water-pitcher" rather than "water-carrier").

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 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.[6] 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.

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

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 signs remain in use as the basis of an ecliptic coordinate system, though modern astronomers have tended to use an equatorial coordinate system since Early Modern times. One can see that the use of the sidereal coordinate remained in use throughout the medieval period, e.g., in "de mensura astrolabii liber" by Hermannus Contractus, who gives the locations of stars in stereographic projection for the construction of an astrolabe. He gives the zodiac coordinate of Antares as 14. Scorpius, equalling a J2000.0 ecliptic longitude of 224° (the 14th degree from the beginning of Scorpius at 210°).

Some authors have drawn parallels between the Babylonian zodiac and the Bible. 19th century theologian E. W. Bullinger interpreted the creatures appearing in the books of Ezekiel and Revelation as the middle signs of the four quarters of the Zodiac,[7][8] with the Lion as Leo, the Bull is Taurus, the Man representing Aquarius and the Eagle standing in[9] Some authors have linked the 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.[10][11] 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.

The twelve signs

The symbols used in Western astrology to represent the astrological signs

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.

no. symbol long. Latin name English translation Greek name Sanskrit name Sumero-Babylonian name[12]
1 ♈ 0° Aries The Ram Κριός Meṣa MUL LUḪUN.GA "The Agrarian Worker", Dumuzi
2 ♉ 30° Taurus The Bull Ταῦρος Vṛṣabha MULGU4.AN.NA "The Steer of Heaven"
3 ♊ 60° Gemini The Twins Δίδυμοι Mithuna MULMAŠ.TAB.BA.GAL.GAL "The Great Twins" (Lugalgirra and Meslamta-ea)
4 ♋ 90° Cancer The Crab Καρκῖνος Karka MULAL.LUL "The Crayfish"
5 ♌ 120° Leo The Lion Λέων Siṃha MULUR.GU.LA "The Lion"
6 ♍ 150° Virgo The Virgin Παρθένος Kanyā MULAB.SIN "The Furrow"; "The Furrow, the goddess Shala's ear of corn"
7 ♎ 180° Libra The Scales Ζυγός Tula zibanitum "The Scales"
8 ♏ 210° Scorpio The Scorpion Σκoρπιός Vṛścika MULGIR.TAB "The Scorpion"
9 ♐ 240° Sagittarius Centaur The Archer Τοξότης Dhanus MULPA.BIL.SAG, Nedu "soldier"
10 ♑ 270° Capricorn "Goat-horned" (The Sea-Goat) Αἰγόκερως Makara MULSUḪUR.MAŠ "The Goat-Fish"
11 ♒ 300° Aquarius The Water Bearer Ὑδροχόος Kumbha MULGU.LA "The Great One", later qâ "pitcher"
12 ♓ 330° Pisces Fish Ἰχθεῖς Mīna MULSIM.MAḪ "The Tail of the Swallow", later DU.NU.NU "fish-cord"

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.

There is also a 13th star/ zodiac sign called Ophiuchus. Of the 13 zodiacal constellations (constellations that contain the Sun during the course of the year), Ophiuchus is the only one not counted as an astrological sign. Ophiuchus is depicted as a man grasping a serpent. Ophiuchus is one of the 88 constellations and was also one of the 48 listed by Ptolemy. Ophiuchus was formerly referred to as Serpentarius, the former originating in Greek and the latter in Latin, both meaning "serpent-holder".

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.[13]

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 is already recognized in Ptolemy's Almagest. This constellation, Ophiuchus is situated between November 30 and December 17. Ophiuchus is not recognised as a general Zodiac.

Table of dates

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

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.[14] 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.[15] In the long term, if the Gregorian calendar isn't reformed, the equinox will move to earlier dates: it will fall on 18 March for the first time in AD 4092.

Sign Constellation[16][17]
Name Symbol Tropical zodiac
(2011, UTC)		 Sidereal zodiac
(Jyotisha) (2011, UTC)[18]		 Name IAU constellation boundaries (2011) Solar stay Brightest star
Aries Aries 20 March – 20 April 14 April – 1 May Aries 19 April – 14 May 25.5 days Hamal
Taurus Taurus 20 April – 21 May 14 May – 1 June Taurus 14 May – 21 June 38.2 days Aldebaran
Gemini Gemini 21 May – 21 June 14 June – 31 July Gemini 21 June – 21 July 29.3 days Pollux
Cancer Cancer 21 June – 23 July 14 July – 1 August Cancer 21 July – 11 August 21.1 days Al Tarf
Leo Leo 23 July – 23 August 14 August – 31 September Leo 11 August – 17 September 36.9 days Regulus
Virgo Virgo 23 August – 23 September 13 September – 30 October Virgo 17 September – 31 October 44.5 days Spica
Libra Libra 23 September – 23 October 14 October – 31 November Libra 31 October – 21 November 21.1 days Zubeneschamali
Scorpio Scorpio 23 October – 22 November 13 November – 30 December Scorpius 21 November – 30 November 8.4 days Antares
Serpentarius Serpentarius n/a Ophiuchus 30 November – 18 December 18.4 days Rasalhague/ Alpha Ophiuchi
Sagittarius Sagittarius 22 November – 22 December 14 December – 2 January Sagittarius 18 December – 21 January 33.6 days Kaus Australis
Capricorn Capricornus 22 December – 20 January 13 January – 1 February Capricornus 21 January – 17 February 27.4 days Deneb Algedi
Aquarius Aquarius 20 January – 19 February 12 February – 2 March Aquarius 17 February – 12 March 23.9 days Sadalsuud
Pisces Pisces 19 February – 20 March 14 March – 1 April Pisces 12 March – 19 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 you live, the greater the difference. Signs are known as of "long" or "short" ascension.[19]

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 choice of origin for the sidereal coordinate system is known as the ayanamsa, a Sanskrit word.

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. Along with the twelve original constellations, the boundaries of a thirteenth constellation, Ophiuchus (the serpent bearer), were set by astronomers within the bounds of the zodiac.

Mnemonics for the zodiac

A traditional mnemonic:[20]

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:[21]

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.[22]

(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)

See also

References

  1. ↑ see MUL.APIN. See also Lankford, John History of Astronomy Routledge 1996 ISBN 978-0-8153-0322-0P.43 [1]
  2. ↑ OED, citing J. Harris, Lexicon Technicum (1704): "Zodiack of the Comets, Cassini hath observed a certain Tract [...] within whose Bounds [...] he hath found most Comets [...] to keep."
  3. ↑ Powell 2004
  4. ↑ Hugh Thurston, Early Astronomy, (New York: Springer-Verlag, 1994), p. 135-137.
  5. ↑ "Scientifically Dating the Constellations". Johnpratt.com. 2001-12-29. http://www.johnpratt.com/items/docs/constellations_date.html. Retrieved 2010-06-02. 
  6. ↑ Derek and Julia Parker, Ibid, p16, 1990
  7. ↑ E.W. Bullinger, The Witness of the Stars
  8. ↑ D. James Kennedy, The Real Meaning of the Zodiac.
  9. ↑ Richard Hinckley Allen, Star Names: Their Lore and Meaning, Vol. 1 (New York: Dover Publications, 1899, p. 213-215.) argued for Scorpio having previously been called Eagle. for Scorpio.
  10. ↑ Ernest L. Martin, The Birth of Christ Recalculated (Pasadena, California: Foundation for Biblical Research, second ed., 1980), p. 167ff.
  11. ↑ D. Guthrie, J.A. Motyer (ed.), The New Bible Commentary (Grand Rapids: William B. Eerdmans Publishing Co., third ed., 1970) p. 173.
  12. ↑ MUL.APIN; Peter Whitfield, History of Astrology (2001); W. Muss-Arnolt, The Names of the Assyro-Babylonian Months and Their Regents, Journal of Biblical Literature (1892).
  13. ↑ 30.4368 SI days or 2629743 seconds in tropical astrology and 30.4380 SI days or 2629846 seconds in sidereal astrology on average (the time spent by the Sun in each sign varies slightly due to the eccentricity of the Earth's orbit).
  14. ↑ The Gregorian calendar is built to satisfy the First Council of Nicaea, which placed vernal equinox is on 21 March, but it is not possible to keep it on a single day within a reasonable system of leap days.
  15. ↑ See Jean Meeus, Astronomical Tables of the Sun, Moon, and Planets, 1983 published by Willmann-Bell, Inc., Richmond, Virginia. The date in other time zones may vary.
  16. ↑ "Astronomical Almanac Online!(subscribers) U.S. Naval Observatory 2008". Asa.usno.navy.mil. http://asa.usno.navy.mil/SecC/Section_C.html. Retrieved 2010-06-02. 
  17. ↑ IAU concluded in 1977
  18. ↑ assuming an ayanamsa of 23.86° as of 2000 according to N. C. Lahiri. The precise value used may vary, but is mostly set close to 24°.
  19. ↑ Julia Parker "The Astrologer's Handbook", pp 10, Alva Press, NJ, 2010
  20. ↑ Project Gutenberg ebook "An Alphabet Of Old Friends"; see Z for Zodiac.
  21. ↑ Rey, H.A. (1952). The Stars, Houghton Mifflin.
  22. ↑ Mnemonic: Zodiac Signs "Mnemonic: Zodiac Signs"
Astronomy | Constellations of the Zodiac
Aries Taurus Gemini Cancer Leo Virgo Libra Scorpius Ophiuchus Sagittarius Capricornus Aquarius Pisces
Astrology | Signs of the Zodiac
Aries Taurus Gemini Cancer Leo Virgo Libra Scorpio Sagittarius Capricorn Aquarius Pisces
Aries.svg Taurus.svg Gemini.svg Cancer.svg Leo.svg Virgo.svg Libra.svg Scorpio.svg Sagittarius.svg Capricorn.svg Aquarius.svg Pisces.svg
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