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refers to a pure calendrical cycle, as there are no equivalent constellations linked
to it like the Western or Indian zodiacs. 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. Thus, twelve cycles of the moon - or months - coincided
with one solar year, making twelve a natural choice.
The majority of
Western astrologers base their work on the tropical zodiac which
evenly divides the ecliptic into 12 segments of 30 degrees each. The
Sun's position at the March equinox, zero degrees Aries, marks the
beginning of the zodiac. The zodiacal signs in this system bear no
relation to the constellations of the same name but stay aligned to
the months and seasons. The tropical zodiac is used as a historical
coordinate system in astronomy.
Practitioners of
the Jyotish (Hindu) 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. The sidereal zodiac is computed from the tropical
zodiac by adding an offset called ayanamsa. This offset changes with
the precession of the equinoxes. |
