Aquarius, illumination from a Book of
Hours, Italian, c. 1475;
in the Pierpont Morgan Library, New York City
The zodiac, is a belt around the heavens extending 9 on either side of the ecliptic, the plane of the earth's orbit and of the sun's apparent annual path. The orbits of the moon and of the principal planets (except Pluto) also lie entirely within the zodiac. The 12 astrological signs of the zodiac are each considered to occupy 1/12 (or 30 ) of its great circle. 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 one constellation (Ophiuchus) that is not considered a member of the zodiac.
Because most of the constellations through which the ecliptic passes represent animals, the ancient Greeks called its zone zodiakos kyklos, "circle of animals," or ta zodia, "the little animals." The size and number of zodiacal constellations varied in antiquity and became fixed only with the development of mathematical astronomy. The list below gives the constellations of the zodiac, with the dates of the sun's passage through them in the era when their boundaries were fixed. These dates are still used for the astrological signs, though precession of the equinoxes has shifted the constellations eastward; e.g., on January 1 the direction of the sun is now in Sagittarius instead of Capricornus. The history of the symbols is unknown; they seem to appear first in Greek manuscripts of the late Middle Ages.
Aries (Ram): March 21-April 19 Taurus (Bull): April 20-May 20 Gemini (Twins): May 21-June 21 Cancer (Crab): June 22-July 22 Leo (Lion): July 23-Aug. 22 Virgo (Virgin): Aug. 23-Sept. 22 Libra (Balance): Sept. 23-Oct. 23 Scorpius (Scorpion): Oct. 24-Nov. 21 Sagittarius (Archer): Nov. 22-Dec. 21 Capricornus (Goat): Dec. 22-Jan. 19 Aquarius (Water Bearer): Jan. 20-Feb. 18 Pisces (Fish): Feb. 19-March 20