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Zodiac

A celestial coordinate system dividing the ecliptic into 12 signs.

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The zodiac is a belt-shaped region of the sky extending about 8° north and south of the ecliptic, the Sun's apparent annual path.[1] The Moon and the brightest planets travel along paths that fall within this belt.[1] The zodiac's 12 signs each span 30° of celestial longitude, and they roughly match the constellations Aries, Taurus, Gemini, and others.[1][2]

Quick Facts

Origin
Babylonian astronomy, 1st millennium BC
Field
Astronomy, astrology
Known for
Division of the ecliptic into 12 zodiac signs
Associated cultures
  • Babylonian
  • Greek
  • Hindu
  • Roman
Key text
Ptolemy's Almagest (2nd century AD)

Facts from the source article.

Key facts and history

Babylonian astronomers divided the ecliptic into 12 equal signs around the end of the 5th century BC, creating the first known celestial coordinate system.[3] According to modern astrophysical calculations, the zodiac was introduced between 409 and 398 BC, during Persian rule.[3] Babylonian astronomers fixed the zodiac in relation to stars, placing the beginning of Cancer at the "Rear Twin Star" (β Geminorum).[3] The zodiac was in use by the Roman era, based on concepts inherited from Babylonian astronomy of the Chaldean period.[4]

Ptolemy's 2nd century AD work, the Almagest, contains a description of how the zodiac was constructed.[4] Hypsicles of Alexandria (fl. 190 BC) wrote the Anaphoricus, the oldest surviving Greek text that employs the Babylonian division of the zodiac into 12 signs of 30 degrees each.[5] The Hindu zodiac is sidereal, meaning it is anchored to fixed stars, and its signs share almost identical symbols with those of the Greek zodiac.[6][7]

What the research sources say

The Nautical Almanac and Astronomical Ephemeris for the year 1767 shows the use of zodiac signs as astronomical coordinates, with the "Longitude of the Sun" columns displaying the sign as a digit from 0 to 11.[8][9] Indian astrology makes extensive use of the naksatras, a division of the zodiac into 27 or 28 portions corresponding to the Moon's daily motion.[10] Schmidt notes that many Hellenistic astrologers influenced by Ptolemy favored a tropical zodiac, while the earliest Hellenistic astrologers' choice between sidereal and tropical remains unresolved.[10] The Nautical Almanac for 1767 shows that the practice of measuring celestial longitude within individual signs was still in use at that time.[8][9]

References

  1. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: "zodiac", Oxford Dictionaries (original not read by us) en.wikipedia.org
  2. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Because the signs are each 30° in longitude but constellations have irregular shapes, and because of precession, they do not correspond exactly to the boundarie; Noble, "Papers communicated to the Association. The Signs of the Zodiac.", Journal of the British Astronomical Association, 1902, p. 242–244 (original not read by us) en.wikipedia.org
  3. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Ossendrijver, "The Encyclopedia of Ancient History", 2013; Britton, "Studies in Babylonian lunar theory: part III. The introduction of the uniform zodiac", Archive for History of Exact Sciences, 2010, p. 617–663; Steele, "A Brief Introduction to Astronomy in the Middle East", Saqi, 2012 (we also read that source) en.wikipedia.org
  4. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Lankford, "History of Astronomy: An Encyclopedia", Taylor & Francis, 1997, p. 43; Ptolemy, "The Almagest", Princeton University Press, 1998 (original not read by us) en.wikipedia.org
  5. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Montelle, "The Circulation of Astronomical Knowledge in the Ancient World", Brill, 2016, p. 287–315; Saliba, "A History of Arabic Astronomy: Planetary Theories During the Golden Age of Islam", New York University Press, 1994, p. 67; Parker, "The New Compleat Astrologer", Crescent Books, 1990, p. 16; Graßhoff, "The History of Ptolemy's Star Catalogue", Springer, 1990, p. 73; Evans, "Geminos's Introduction to the Phenomena", Princeton University Press, 2006, p. 113; Ashmand, "Ptolemy's Tetrabiblos", Astrology Classics, 2011, p. 37 (I.XXV) (origina en.wikipedia.org
  6. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Mill, "The History of British India", Baldwin, Cradock, and Joy, 1817, p. 409 (original not read by us) en.wikipedia.org
  7. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Schmidt, "The Relation of Hellenistic to Indian Astrology", Project Hindsight; Dalal, "Hinduism: An Alphabetical Guide", Penguin Books India, 2010, p. 89 (we also read that source) en.wikipedia.org
  8. Nautical Almanac and Astronomical Ephemeris for the year 1767. London: Board of Longitude, 1766.. facts only, no text reused. archive.org
  9. Wikipedia, "Zodiac" (CC BY-SA 4.0), which cites: Nautical Almanac and Astronomical Ephemeris for the year 1767. London: Board of Longitude, 1766. (we also read that source) en.wikipedia.org
  10. Schmidt, "The Relation of Hellenistic to Indian Astrology", Project Hindsight. facts only, no text reused. projecthindsight.com

Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Zodiac (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.

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Sources

Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.

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