Sidereal and tropical astrology

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In astrology, sidereal and tropical are terms that refer to two different systems of ecliptic coordinates used to divide the ecliptic into twelve "signs". Each sign is divided into 30 degrees, making a total of 360 degrees.[1] The terms sidereal and tropical may also refer to two different definitions of a year, applied in sidereal solar calendars or tropical solar calendars.

While sidereal systems of astrology calculate twelve zodiac signs based on the observable sky and thus account for the apparent backwards movement of fixed stars of about 1 degree every 72 years from the perspective of the Earth due to the Earth's axial precession, tropical systems consider 0 degrees of Aries as always coinciding with the March equinox (known as the spring equinox in the Northern Hemisphere) and define twelve zodiac signs from this starting point, basing their definitions upon the seasons and not upon the observable sky wherein the March equinox currently falls in Pisces due to the Earth's axial precession.[2][3][4] These differences have caused sidereal and tropical zodiac systems, which were aligned around 2,000 years ago when the March equinox coincided with Aries in the observable sky, to drift apart over the centuries.[5][6][7]

Sidereal astrology accounts for the Earth's axial precession and maintains the alignment between signs and constellations via corrective systems known as ayanamsas (Sanskrit: 'ayana' "movement" + 'aṃśa' "component"), whereas tropical astrology, to reiterate, is based upon the seasonal cycle of the Northern hemisphere and does not take axial precession into consideration. Though tropical astrology typically considers the zodiac of the Northern Hemisphere to be applicable without change to the Southern hemisphere, a small number of tropical astrologers modify the zodiac to reflect seasons in the Southern hemisphere, taking Libra as the sign that coincides with the spring equinox instead of Aries.[3][8][9]

Ayanamsa systems used in Hindu astrology (also known as Vedic astrology) include the Lahiri ayanamsa and the Raman ayanamsa, of which the Lahiri ayanamsa is the most widely used.[10] The Fagan-Bradley ayanamsa is an example of an ayanamsa system used in Western sidereal astrology.[10] As of 2020, sun signs calculated using the Sri Yukteswar ayanamsa were around 23 degrees behind tropical sun signs.[8] Per these calculations, persons born between March 12 – April 12, for instance, would have the sun sign of Pisces.[8] Per tropical calculations, in contrast, persons born between March 21 – April 19 would have the sun sign of Aries.[11]

Precession of 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.

Astronomic zodiac[edit]

A small number of sidereal astrologers[who?] 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.

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, as the first sign rather than of Aries. The IAU defined the constellation boundaries without consideration of astrological purposes.

The dates the Sun passes through the 12 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.

Symbol Constellation Tropical zodiac dates[12] Sidereal zodiac dates[13][14][15]
(Lahiri ayanamsa)
Based on IAU boundaries[16]
Aries March 22 – April 20 April 14 – May 14 April 18 – May 13
Taurus April 21 – May 21 May 15 – June 15 May 13 – June 21
Gemini May 22 – 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 23 September 17 – October 17 September 16 – October 30
Libra September 24 – October 23 October 18 – November 16 October 30 – November 23
Scorpio October 24 – November 22 November 17 – December 15 November 23 – November 29
Ophiuchus[a] November 29 – December 17
Sagittarius November 23 – December 22 December 16 – January 14 December 17 – January 20
Capricorn December 23 – January 22 January 15 – February 12 January 20 – February 16
Aquarius January 23 – February 20 February 13 – March 14 February 16 – March 11
Pisces February 21 – March 21 March 15 – April 13 March 11 – April 18
  1. ^ Ophiuchus is not a sign in traditional forms of tropical and sidereal astrology, and only appears in a few forms of astrology which use the IAU-defined constellations.

See also[edit]

References[edit]

  1. ^ "The Tropical, Sidereal & Constellational Zodiacs: the Power of World View". www.renaissanceastrology.com. Archived from the original on March 20, 2022. Retrieved July 29, 2020.
  2. ^ Subramanian, Vijaya. "Sidereal and Tropical Zodiac – Vijaya Jyoti". Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  3. ^ a b galacticcenter (October 10, 2016). "What is Vedic Astrology?". Galactic Center with Joni Patry. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  4. ^ Taya. "Understanding Sidereal Charts". astro-charts.com. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  5. ^ Subramanian, Vijaya. "Sidereal and Tropical Zodiac – Vijaya Jyoti". Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  6. ^ galacticcenter (October 10, 2016). "What is Vedic Astrology?". Galactic Center with Joni Patry. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  7. ^ Vallée, Guylaine (March 1, 2020). "What's Your Vedic Astrological Sign?". Birla Vedic Center. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  8. ^ a b c Vallée, Guylaine (March 1, 2020). "What's Your Vedic Astrological Sign?". Birla Vedic Center. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  9. ^ Mystic (October 20, 2020). "The Real Southern Hemisphere Astrology". Mystic Medusa Astrology. Retrieved February 23, 2023.
  10. ^ a b "Ayanamshas in Sidereal Astrology". www.astro.com. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  11. ^ "Zodiac Sign Dates: What Are The Dates for Every Star Sign?". Astrostyle: Astrology and Daily, Weekly, Monthly Horoscopes by The AstroTwins. September 28, 2016. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  12. ^ "Zodiac Sign Dates: What Are The Dates for Every Star Sign?". Astrostyle: Astrology and Daily, Weekly, Monthly Horoscopes by The AstroTwins. Archived from the original on August 7, 2020. Retrieved July 29, 2020.
  13. ^ "Sidereal Astrology Explained". Retrieved February 23, 2023.
  14. ^ "Western Sidereal Astrology Is Real Astrology:". November 28, 2008.
  15. ^ "Free Sidereal Birth Chart Calculator | Cafe Astrology .com". cafeastrology.com.
  16. ^ "New astrological sign: Professor finds horoscopes may be a little off kilter". Los Angeles Times. Times. January 14, 2011. Archived from the original on January 19, 2011.

External links[edit]