In the sidereal zodiac the signs of the zodiac overlap extensively with the star constellations which they were named for. The sidereal zodiac is most commonly associated with Indian astrology (also known as Vedic or jyotish astrology).
Western astrologers generally work with the tropical zodiac where the start of the zodiac at the spring equinox and 0 degrees Aries is defined as the point at which the sun crosses the celestial equator in a northerly direction on its apparent path around the earth.
There is a less clear definition in the sidereal zodiac. The precession of the equinoxes causes the sidereal zodiac to move one degree every 72 years in relation to the tropical zodiac. The standard ayanamsha value or divergence between the two zodiacs was 23 degrees, 51 minutes and 11 seconds on first of January 2000 (according to N.C. Lahiri). Using this value, 0 degrees of Aries in the tropical zodiac is equivalent to 6 degrees, 8 minutes and 49 seconds Pisces in the sidereal zodiac. However, some ayanamshas deviate from this value by several degrees, such that a planet at tropical 27 degrees of a sign could be at 0 degrees of the sidereal sign.
Both the tropical and sidereal zodiacs are divided into twelve equal segments of exactly thirty degrees. The sequence of signs is identical, although their interpretations vary somewhat between India and the West.
- For The Sidereal Zodiac (For & Against: The Zodiac Debate; Kenneth Bowser, 1997/ 2005; Skyscript)
- Western Sidereal Astrology (three parts, originally 2007; Bowser)
- Vedic Astrology - critically examined (Dieter Koch, 2013; Astrodienst)
- For calculations select Option "sidereal" (Extended Chart Selection; there are about thirty different variants)
- Ayanamshas in Sidereal Astrology The different systems explained by Dieter Koch (2016).
- Solunars (Forum for Sidereal Astrology; James Eshelman)
- James Eshelman: Sidereal Mundane Astrology (Download E-book, 2013; scribd.com)
Notes and References
- At Kanipakam, Andhra Pradesh/ India