The zodiac

The zodiac is the belt or band of constellations through which the Sun, Moon, and planets move on their journey across the sky.

Astrologers noted these constellations and so attached a particular significance to them. Over time they developed the system of twelve signs of the zodiac, based on twelve of the constellations they considered to be particularly important.

The Western and Indian zodiac signs have a common origin in the tradition of horoscopic astrology, and so are very similar in meaning. The common choice of twelve zodiac signs is understandable when it is considered that the interaction of the Sun and Moon was central to all forms of astrology.

The majority of Western astrologers base their work on the tropical zodiac which divides the sky into twelve equal segments of 30 degrees each, beginning with the first point of Aries, the point where the line of the earth's celestial equator and the ecliptic (the Sun's path through the sky) meet at the northern hemisphere spring equinox.
Practitioners of the Indian astrological tradition and a minority of Western astrologers use the sidereal zodiac. This zodiac uses the same evenly divided ecliptic but approximately stays aligned to the positions of the observable constellations with the same name as the zodiacal signs.