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Sidereal astrology
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Sidereal astrology is the system of astrology used by some Western and all Jyotish astrologers who base their interpretation around the use of the sidereal zodiac. Its primary feature is that the signs of the zodiac align to the sky constellations of the same name. The signs therefore run between dates which are different from the tropical zodiac used in the West. For example, Aries runs from March 21 to April 20 in the tropical zodiac but extends from April 14 to May 14 in the sidereal (although the precise dates may vary depending on the sidereal system used).
In effect, in most Western astrology the link between sign and sky constellation has been broken, whereas in Sidereal astrology it remains of paramount importance.
It was introduced to the West by the Irish astrologer Cyril Fagan in 1944 and is practiced by a minority of Western astrologers.
BackgroundThe 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 c. 130 BC by Hipparchus and known to Ptolemy, results in a shift between the two systems of about one degree every 70 years.
The 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 astronomical 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 ).
Vedic astrologyAncient Vedic astrology is based on the sidereal or visible zodiac, accounting for the shift of the equinoxes by a correction called ayanamsa. The difference between the Vedic and the Western zodiacs is currently around 24 degrees. This corresponds to a separation of c. 1700 years, when the vernal equinox was approximately at the center of the constellation Pisces and the tropical zodiac coincided with the sidereal one. The separation likely took place in the centuries following Ptolemy, apparently going back to Indo-Greek transmission of the system. The ayanamsa correction has always been made in Vedic astrology, whose existence spans around five thousand years.
Cyril FaganCyril Fagan assumes the origin of the zodiac in 786 BCE, when the vernal equinox lay somewhere in mid-Aries, based on a major conjunction that occurred that year, corresponding to a difference of some 39 degrees or days.
Signs vs. astronomical constellations of the zodiacNearly all astrologers, tropical and sidereal, agree that the ecliptic should be divided into twelve equal segments to form the zodiac; they differ on where the zodiac begins.
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 BCE, this results in an identical system as that of the classical tropical zodiac, shifted by 25.5 days, i.e., if in tropical astrology, Aries is taken to begin at March 21, sidereal Aries will begin on April 15.
The 13 astronomical constellations of the eclipticA small number of sidereal astrologers wish to include other constellations, such as Ophiuchus, in their zodiac and use 13 signs instead of 12. This results in a system completely unrelated to the zodiac as described by Ptolemy. While Ptolemy noted that Ophiuchus is in contact with the ecliptic, he was aware that the twelve signs were just conventional names for 30 degrees segments (especially since the Aries sign had ceased to be in contact with the Aries constellation already in his time).
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 of astrological purposes.
The dates the Sun passes through the 13 astronomical constellations of the ecliptic are listed below, accurate to the year 2002. The dates will increment by one day every 70½ years, and already several have changed. The corresponding tropical and sidereal dates are given as well.
| Constellation | Tropical date | Sidereal Date | Sun is in constellation |
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| | Aries | March 21 - April 20 | April 15 - May 15 | April 19 - May 13 | | | Taurus | April 21 - May 21 | May 16 - June 15 | May 14 - June 19 | | | Gemini | May 22 - June 23 | June 16 - July 15 | June 20 - July 20 | | | Cancer | June 24 - July 23 | July 16 - August 15 | July 21 - August 9 | | | Leo | July 24 - August 23 | August 16 - September 15 | August 10 - September 15 | | | Virgo | August 24 - September 22 | September 16 - October 15 | September 16 - October 30 | | | Libra | September 23 - October 23 | October 16 - November 15 | October 31 - November 22 | | | Scorpius | October 24 - November 22 | November 16 - December 15 | November 23 - November 29 | | | Ophiuchus | | | November 30 - December 17 | | | Sagittarius | November 23 - December 21 | December 16 - January 14 | December 18 - January 18 | | | Capricornus | December 22 - January 19 | January 15 - February 14 | January 19 - February 15 | | | Aquarius | January 20 - February 18 | February 15 - March 14 | February 16 - March 11 | | | Pisces | February 19 - March 20 | March 15 - April 14 | March 12 - April 18 |
The 21 zodiacal constellations of the planetsBecause of their inclination from the ecliptic, the planets are not restricted to the 13 constellations of the ecliptic. The eight planets pass through 21 constellations. Thus there are 21 astronomical constellations of the zodiac. These are, in addition to the 13 constellations listed above, Cetus, Corvus, Crater, Hydra, Orion, Pegasus, Scutum, and Sextans.
See also
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