An Etymological Dictionary of Astronomy and Astrophysics

An imaginary belt around the heavens extending about 9° on either side of the → ecliptic. The orbits of the Moon and of the principal planets also lie entirely within the zodiac.
The zodiac was created during the first half of the first millennium B.C. by Babylonian astronomers, who divided it into 12 constellations (→ sign of the zodiac) each considered to occupy 1/12, or 30°, of its great circle. They were named after living creatures, with the exception of Libra:
→ Aries, → Taurus, → Gemini, → Cancer, → Leo, → Virgo, → Libra, → Scorpius, → Sagittarius, → Capricornus, → Aquarius, → Pisces. However, as a result of → precession, these signs no longer correspond to the astronomical constellations in which the Sun actually appears. The constellations are irregular in size and shape, and the Sun regularly passes through 13 constellations as it moves along the ecliptic. The additional 13th constellation is → Ophiuchus, situated between → Scorpius and → Sagittarius. See also → dodekatemorion.

Etymology (EN): From M.E. zodiaque, from O.Fr. zodiaque, from L. zodiacus, from Gk. zodiakos (kyklos) “zodiac (circle),” literally “circle of little animals,” from zodiaion, diminutive of zoion “animal,” literally “a living being,” from PIE base *gwei- “to live, life;” cognate with Pers. zist, → bio-.

Etymology (PE): Borjgân, from borj, → sign of the zodiac,

• -gân suffix denoting multiplicity, order, organization.