Signs of the Zodiac
The zodiac is an imaginary belt in the sky within which the sun, moon, and planets appear to move against the background of the fixed stars. This belt was divided by ancient astronomers and astrologers into twelve equal parts, referred to in English as signs of the zodiac or houses of heaven or simply houses, each named after a constellation within it.
To an observer on Earth the sun appears to move slowly across the celestial sphere, i.e., an imaginary sphere which encloses the universe and on the surface of which all the heavenly bodies appear to be projected. This apparent movement of the sun against the background of the fixed stars is of course a consequence of the earth's revolution around the sun, and so in the course of a year, i.e., a single revolution around the sun by the earth, the sun appears to make a complete circuit of the celestial sphere. (In the same way the 'more erratic' course of the planets against the background of the fixed stars - the word 'planet' comes from the Greek πλάνης‚ (planes), which means 'wanderer' - is a consequence of their and the earth's revolving around the sun in different orbits and at different speeds.) The apparent path of the sun on the celestial sphere is known as the ecliptic, and the zodiac is an imaginary belt on the celestial sphere extending about 8° either side of the ecliptic. Not only the apparent path of the sun but those of the moon and the planets are always within this belt.
The twelve equal parts into which the zodiac has been divided, i.e., the signs of the zodiac, correspond to twelve equal stages of the sun's apparent annual circuit of the celestial sphere and therefore to twelve equal parts of our terrestrial year. The signs are usually referred to by their Latin names, which, together with their English equivalents, are as follows:
- Aries (The Ram) - March 21st-April 20th
- Taurus (The Bull) - April 21st-May 20th
- Gemini (The Twins) - May 21st-June 21st
- Cancer (The Crab) - June 22nd-July 22nd
- Leo (The Lion) - July 23rd-August 22nd
- Virgo (The Maiden) - August 23rd-September 22nd
- Libra (The Scales) - September 23rd-October 22nd
- Scorpio (The Scorpion) - October 23rd-November 21st
- Sagittarius (The Archer) - November 22nd-December 20th
- Capricornus (The Goat) - December 21st-January 19th
- Aquarius (The Water-carrier) - 22nd January-February 18th
- Pisces (The Fishes) - February 19th-March 20th.
The dates associated with the signs are the periods during which the sun was in the corresponding sign when these dates were originally assigned, i.e., at that time the sun entered Aries at the spring equinox, March 21st. However, owing to the precession of the equinoxes, i.e., the slightly earlier occurrence of the equinox each year as a result of the slow westward shift of the equinoctial point on the ecliptic, these dates no longer precisely match the periods during which the sun is in the corresponding sign - in fact on March 21st the sun is now in Pisces. Nonetheless western astrologers continue to use the traditional set of dates.
- Etymological note: The word 'zodiac' comes originally from the Greek ζῳδιακός‚ (zodiakos), an adjective from ζῳδιον (zodion), 'a small figure or sign of the zodiac' (a diminutive of ζῷον, zoon, 'animal or living creature'). Ancient astrologers, as do their contemporaries, represented the zodiac as a circle, divided into twelve equal segments corresponding to the twelve signs, each segment containing a figure or constellation representing the sign. Hence the zodiac was known as the ζῳδιακός κύκλος‚ (zodiakos kuklos), 'the circle of small figures'.
- See also Names of the Planets.
