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Sidereal and tropical astrology

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Sidereal and tropical are astrological terms used to describe two different definitions of a year. They are also used as terms for two systems of ecliptic coordinates used in astrology. Both divide the ecliptic into twelve "signs" that are divided into 30 degrees each (making a total of 360 degrees) and named after constellations,[1] but while the sidereal system defines the signs relative to the apparent backwards movement of fixed stars of about 1 degree every 72 years as per our perspective from Earth,[2] the tropical zodiac fixes the vernal point (also known as vernal equinox or March equinox in the Northern hemisphere) to 0 degrees of Aries, without taking the precession of equinoxes into account, and defines the rest of the zodiac from this point.[3][4]

Because of the sidereal zodiac using a correction called ayanamsa to account for the precession of equinoxes, the two systems do not remain fixed relative to each other and drift apart by about 1 degree per 72 years.[2] The current difference stands at about 23 degrees and 50 minutes.[2] Ayanamsa systems are used in both Vedic sidereal astrology and in Western sidereal astrology.[3] The tropical system is thought to have been adopted during the Hellenistic period and remains prevalent in Western astrology.[3]

Tropical TraditionsEdit

Precession of the equinoxes, the changing position of the vernal equinox over the course of about 25,800 years. The yellow line is a section of the ecliptic, the apparent path the Sun appears to follow over the course of an Earth year. The purple line is the celestial equator, the projection of Earth's equator onto the celestial sphere. The point (red) where these two lines cross is the vernal equinox. In 1500 BCE, it was near the end of Aries; in 500 BCE, it was near the beginning of Aries; and in 1000 to 2500 CE Pisces.

The tropical zodiac is thought to have been used by Western astrologers since about 100 B.C. and does not correspond to the visible zodiac.[1] Instead, it is defined based on seasons and their relationship to the cycles of the Sun.[1][2] Seasons are defined as seen from the Northern hemisphere and the March equinox has a fixed relationship to 0 degrees of Aries, regardless of the astronomical position of the Sun with respect to constellations as seen from the Earth.[3][4][5] This means that during the March equinox, the Sun is always seen as being "in" Aries.[4] Some schools of thought have emerged to account for seasons as seen from the Southern hemisphere, where they are more or less in reverse.[5] For instance, in the Northern hemisphere, the March equinox occurs during Spring, whereas in the Southern hemisphere, it occurs in Autumn.[5]

Sidereal traditionsEdit

Hindu astrologyEdit

Traditional Hindu astrology, also known as Vedic astrology, uses a sidereal system of zodiac and accounts for the precession of the equinoxes using a system of correction called ayanamsa, which allows it to be more accurately reflective of current astronomical trends than the tropical zodiac.[6][7][2] There are various types of ayanamsa that are in use, such as Lahiri Ayanamsa and Raman Ayanamsa.[3]

In contrast to the tropical zodiac which has stuck with 0 degrees of Aries as the vernal point (the location of the Sun during the March equinox),[3] the sidereal zodiac currently uses approximately 6 degrees of Pisces as the vernal point as per its corrective calculations, putting it almost a full sign (or about 24 degrees) behind the tropical zodiac.[7] This also puts sidereal calculations[8] of the position of the sun with respect to zodiacal constellations and equinoxes more accurately in keeping with current astronomical calculations[9][10] of the sun's position with respect to the same. Walter Berg's astronomical zodiac, like the sidereal zodiac, lags nearly a full sign behind the tropical zodiac.[9]

The tropical and the sidereal zodiacs were lined up together about 2,000 years ago.[2] Vedic astrology is thought to have been in development from as far back as 5,000 B.C.[11][12]

Sidereal western astrologyEdit

Western sidereal astrology also uses ayanamsa, with the Fagan/Bradley ayanamsa being the most prevalent.[3]

Shifted zodiacEdit

Cyril Fagan assumed the origin of the zodiac to be based on a major conjunction that occurred in 786 BC, when the vernal equinox lay somewhere in mid-Aries[13] corresponding to a difference of some 39 degrees or days.

Astronomic zodiacEdit

A small number of sidereal astrologers do not take the astrological signs as an equal division of the ecliptic, but define their signs based on the actual width of the individual constellations. They also include constellations that are disregarded by the traditional zodiac, but are still in contact with the ecliptic.

Stephen Schmidt, in his 1970 book Astrology 14, introduced a system with additional signs based on the constellations of Ophiuchus and Cetus.[14][15]

In 1995, Walter Berg introduced his 13-sign zodiac, which has the additional sign of Ophiuchus. Berg's system was well received in Japan after his book was translated by radio host Mizui Kumi (水井久美) in 1996.

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. 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 2011. The dates will progress by an increment of one day every 70.5 years. The corresponding tropical and sidereal dates are given as well.

Constellation Tropical date Sidereal Date
Cyril Fagan
Based on IAU boundaries
Walter Berg[10]
  Aries March 21 – April 20 April 15 – May 15 April 18 – May 13
  Taurus April 21 – May 20 May 16 – June 15 May 13 – June 21
  Gemini May 21 – June 21 June 16 – July 16 June 21 – July 20
  Cancer June 22 – July 22 July 17 – August 16 July 20 – August 10
  Leo July 23 – August 23 August 17 – September 16 August 10 – September 16
  Virgo August 24 – September 22 September 17 – October 17 September 16 – October 30
  Libra September 23 – October 23 October 18 – November 16 October 30 – November 23
  Scorpio October 24 – November 22 November 17 – December 16 November 23 – November 29
  Ophiuchus N/A November 29 – December 17
  Sagittarius November 23 – December 22 December 17 – January 15 December 17 – January 20
  Capricorn December 23 – January 20 January 16 – February 14 January 20 – February 16
  Aquarius January 21 – February 18 February 15 – March 15 February 16 – March 11
  Pisces February 19 – March 20 March 16 – April 14 March 11 – April 18

See alsoEdit


  1. ^ a b c "The Tropical, Sidereal & Constellational Zodiacs: the Power of World View". Retrieved 2019-12-05.
  2. ^ a b c d e f Patry, Joni. "Read About You" (Vedic astrology chart calculator with an explanation of the tropical and sidereal zodiac given beneath).
  3. ^ a b c d e f g "Ayanamshas in Sidereal Astrology". Retrieved 2019-12-05.
  4. ^ a b c Taya. "Understanding Sidereal Charts". Retrieved 2019-12-06.
  5. ^ a b c "Astrology: Are Zodiac Signs Reversed In Earth's Southern Hemisphere? - A Whole-Earth, Dual-Sign, 6-sign, or Mirror Zodiac". Retrieved 2019-12-06.
  6. ^ VS (2015-03-28). "Sidereal vs. Tropical". The Art of Vedic Astrology. Retrieved 2019-12-06.
  7. ^ a b Subramanian, Vijaya. "Sidereal and Tropical Zodiac – Vijaya Jyoti". Retrieved 2019-12-06.
  8. ^ Vallée, Guylaine (2017-07-18). "What's Your Vedic Astrological Sign?". Birla Vedic Center. Retrieved 2019-12-06.
  9. ^ a b "What is the zodiac? |". Retrieved 2019-12-06.
  10. ^ a b New astrological sign: Professor finds horoscopes may be a little off kilter a January 14, 2011 article from the Los Angeles Times
  11. ^ Moroney, Alison. "Sidereal versus Tropical astrology".
  12. ^ Rich, Vandana. "How old is Vedic astrology?".
  13. ^
  14. ^ "Modern Living: The Revised Zodiac". Time. 23 November 1970. ISSN 0040-781X.
  15. ^ Schmidt, Steven (1970). Astrology 14. Bobbs-Merrill Company. pp. 6–8.

External linksEdit