Sidereal astrology is the system of astrology used by some western and all Jyotish astrologers which bases their interpretation around the use of the sidereal zodiac. It was introduced to the West by the Irish astrologer Cyril Fagan in 1944 and is practiced by a minority of Western astrologers.
The classical zodiac of Greek astronomy as defined by Ptolemy is tropical in nature, defining the signs relative to vernal equinox regardless of the position of constellations. Western astrology traditionally uses this system.
Sidereal astrology ties its signs of the zodiac to the actual constellations.
The precession of the equinoxes, a phenomenon discovered in ca. 130 BC by Hipparchus and known to Ptolemy, results in a shift between the two systems of about one degree every 70 years.
Vernal equinox lay near the beginning of the Aries constellation around 500 BC, consistent with a Babylonian origin of the system.
While classical tropical astrology is based on the orientation of the Earth relative to the Sun and planets of the solar system, sidereal astrology deals with the position of the Earth relative to both of these as well as the stars of the celestial sphere. The actual positions of certain fixed stars as well as their constellations is an additional consideration in the horoscope. (Over very long astonomical time scales these fixed stars are of course themselves far from stationary).
Some Sidereal astrologers denounce tropical astrologers for failing to relate to the "actual heavens", seeing in this a fundamental degeneration of the subject (Kenneth Bowser, The Traditional Astrologer magazine, (Ascella), Issue 14, May 1997, pp.23-27 *)
Traditional Hindu astrology is sidereal, accounting for the shift of the equinoxes by a correction called ayanamsa. The difference between the Hindu and the Western zodiacs is currently around 24 degrees. This corresponds to a separation of ca. 1700 years, or roughly the centuries following Ptolemy, apparently going back to Indo-Greek transmisson of the system.
At this time, the vernal equinox was approximately at the center of the constellation Pisces.
Thus, most sidereal astrologers simply divide the ecliptic into 12 equal signs of 30 degrees but approximately aligned to the 12 zodiac constellations. Assuming an origin of the system in 786 BC, this results in an identical system as that of the classical tropical zodiac, shifted by 39.5 days, i.e. if in tropical astrology, Aries is taken to begin at 21 March, sidereal Aries will begin on 30 April.
For the purpose of determining the constellations in contact with the ecliptic, the constellation boundaries as defined by the International Astronomical Union in 1930 are used. For example, the Sun enters the IAU boundary of Aries on April 19 at the lower right corner, a position that is still rather closer to the "body" of Pisces than of Aries. Needless to say, the IAU defined the constellation boundaries without consideration for astrological purposes.
The dates the sun passed in front of the thirteen astronomical constellations of the ecliptic in 1977 are as follows. The dates will increment by one day every 70½ years and already several have changed.
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It uses material from the
"Sidereal astrology".
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