Tropical Zodiac

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Clock at St. Marks Basilica in Venice.

The zodiac which begins at the spring equinox. The spring equinox is the point at which the Sun crosses the celestial equator from South to North on its apparent path around the Earth. In the northern hemisphere the spring equinox is equivalent to 0 degrees of Aries and the point opposite (the autumnal equinox) to 0 degrees Libra. When the Sun is at either 0 degrees of Aries or 0 degrees of Libra the length of daylight hours are the same for every location on the Earth's surface.

The other important "turning points" on the Sun's apparent path around the Earth are the two solstices: the summer solstice in the northern hemisphere at 0 degrees of Cancer and the winter solstice at 0 degrees of Capricorn. This is where the tropical zodiac gets its name: The tropical zodiac is characterised by these four critical points (Greek tropoi.)

The precession of the equinoxes causes the spring equinox to move backwards through the zodiac which is a basic difference between the tropical zodiac and the sidereal zodiac where the latter does not move with relation to the tropical one over longer periods of time. The sidereal zodiac approximately overlaps the constellations for which the signs were named, but because the constellations are either larger or smaller than 30 degrees on the ecliptic the correspondence is imprecise. The discrepancy (called Ayanamsha in Vedic astrology) between the two is currently around 24 degrees.

Western astrology usually works with the tropical zodiac and Indian astrology with the sidereal one.

See also