View source for Sidereal and tropical astrology

{{Use mdy dates|date=February 2023}}
{{Short description|Forms of astrology}}
{{Astrology}}

In astrology, ''[[Sidereal time|sidereal]]'' and ''[[Tropical year|tropical]]'' are terms that refer to two different systems of [[Ecliptic coordinate system|ecliptic coordinates]] used to divide the [[ecliptic]] into twelve "[[zodiac signs]]". Each sign is divided into 30 degrees, making a total of 360 degrees.<ref>{{Cite web|title=The Tropical, Sidereal & Constellational Zodiacs: the Power of World View|url=https://www.renaissanceastrology.com/zodiacworldview.html|access-date=July 29, 2020|website=www.renaissanceastrology.com|archive-date=March 20, 2022|archive-url=https://web.archive.org/web/20220320010828/https://www.renaissanceastrology.com/zodiacworldview.html|url-status=live}}</ref> The terms sidereal and tropical may also refer to two different definitions of a year, applied in [[sidereal solar calendar]]s or [[tropical solar calendar]]s.

While sidereal systems of astrology calculate twelve zodiac signs based on the observable sky and thus account for the apparent backwards movement of [[fixed star]]s 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 (astrology)|Aries]] as always coinciding with the [[March equinox]] (known as the [[Spring equinox (northern hemisphere)|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 (astrology)|Pisces]] due to the Earth's axial precession.<ref name=":0">{{Cite web|last=Subramanian|first=Vijaya|title=Sidereal and Tropical Zodiac – Vijaya Jyoti|url=https://vijayajyoti.com/sidereal-and-tropical-zodiac/|access-date=July 29, 2020|language=en|archive-date=August 7, 2020|archive-url=https://web.archive.org/web/20200807091852/https://vijayajyoti.com/sidereal-and-tropical-zodiac/|url-status=live}}</ref><ref name=":12">{{Cite web|last=galacticcenter|date=October 10, 2016|title=What is Vedic Astrology?|url=https://galacticcenter.org/what-is-vedic-astrology/|access-date=July 29, 2020|website=Galactic Center with Joni Patry|language=en-US|archive-date=August 7, 2020|archive-url=https://web.archive.org/web/20200807043953/https://galacticcenter.org/what-is-vedic-astrology/|url-status=live}}</ref><ref>{{Cite web|last=Taya|title=Understanding Sidereal Charts|url=https://astro-charts.com/blog/2017/using-sidereal-charts/|access-date=July 29, 2020|website=astro-charts.com|language=en|archive-date=August 7, 2020|archive-url=https://web.archive.org/web/20200807041301/https://astro-charts.com/blog/2017/using-sidereal-charts/|url-status=live}}</ref> 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.<ref name=":02">{{Cite web |last=Subramanian |first=Vijaya |title=Sidereal and Tropical Zodiac – Vijaya Jyoti |url=https://vijayajyoti.com/sidereal-and-tropical-zodiac/ |url-status=live |archive-url=https://web.archive.org/web/20200807091852/https://vijayajyoti.com/sidereal-and-tropical-zodiac/ |archive-date=August 7, 2020 |access-date=July 29, 2020 |language=en}}</ref><ref name=":122">{{Cite web |last=galacticcenter |date=October 10, 2016 |title=What is Vedic Astrology? |url=https://galacticcenter.org/what-is-vedic-astrology/ |url-status=live |archive-url=https://web.archive.org/web/20200807043953/https://galacticcenter.org/what-is-vedic-astrology/ |archive-date=August 7, 2020 |access-date=July 29, 2020 |website=Galactic Center with Joni Patry |language=en-US}}</ref><ref name=":222">{{Cite web |last=Vallée |first=Guylaine |date=March 1, 2020 |title=What's Your Vedic Astrological Sign? |url=https://www.birla.ca/en/whats-your-vedic-astrological-sign/ |url-status=live |archive-url=https://web.archive.org/web/20200807070828/https://www.birla.ca/en/whats-your-vedic-astrological-sign/ |archive-date=August 7, 2020 |access-date=July 29, 2020 |website=Birla Vedic Center |language=en-US}}</ref>

Sidereal astrology accounts for the Earth's axial precession and maintains the alignment between signs and [[constellation]]s via corrective systems known as [[ayanamsa]]s (Sanskrit: ''<nowiki/>'ayana'<nowiki/>'' "movement" + ''<nowiki/>'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 (astrology)|Libra]] as the sign that coincides with the spring equinox instead of Aries.<ref name=":12" /><ref name=":22">{{Cite web|last=Vallée|first=Guylaine|date=March 1, 2020|title=What's Your Vedic Astrological Sign?|url=https://www.birla.ca/en/whats-your-vedic-astrological-sign/|access-date=July 29, 2020|website=Birla Vedic Center|language=en-US|archive-date=August 7, 2020|archive-url=https://web.archive.org/web/20200807070828/https://www.birla.ca/en/whats-your-vedic-astrological-sign/|url-status=live}}</ref><ref>{{Cite web |last=Mystic |date=October 20, 2020 |title=The Real Southern Hemisphere Astrology |url=https://mysticmedusa.com/planets-in-astrology/the-real-southern-hemisphere-astrology/ |access-date=February 23, 2023 |website=Mystic Medusa Astrology |language=en-US}}</ref>

Ayanamsa systems used in Hindu astrology (also known as [[Vedas|Vedic]] astrology) include the Lahiri ayanamsa and the Raman ayanamsa, of which the Lahiri ayanamsa is the most widely used.<ref name=":32">{{Cite web|title=Ayanamshas in Sidereal Astrology|url=https://www.astro.com/astrology/in_ayanamsha_e.htm|access-date=July 29, 2020|website=www.astro.com|language=en|archive-date=August 7, 2020|archive-url=https://web.archive.org/web/20200807034957/https://www.astro.com/astrology/in_ayanamsha_e.htm|url-status=live}}</ref> The [[Cyril Fagan|Fagan-Bradley]] ayanamsa is an example of an ayanamsa system used in Western sidereal astrology.<ref name=":32" /> As of 2020, [[Sun sign astrology|sun signs]] calculated using the [[Sri Yukteswar]] ayanamsa were around 23 degrees behind tropical sun signs.<ref name=":22" /> Per these calculations, persons born between March 12 – April 12, for instance, would have the sun sign of [[Pisces (astrology)|Pisces]].<ref name=":22" /> Per tropical calculations, in contrast, persons born between March 21 – April 19 would have the sun sign of Aries.<ref>{{Cite web|title=Zodiac Sign Dates: What Are The Dates for Every Star Sign?|url=https://astrostyle.com/zodiac-sign-dates/|access-date=July 29, 2020|website=Astrostyle: Astrology and Daily, Weekly, Monthly Horoscopes by The AstroTwins|date=September 28, 2016 |language=en-US|archive-date=August 7, 2020|archive-url=https://web.archive.org/web/20200807052034/https://astrostyle.com/zodiac-sign-dates/|url-status=live}}</ref>[[File:Equinox positions2.png|thumb|Precession of equinoxes, the changing position of the [[Equinox (celestial coordinates)|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 [[Tropical year|Earth year]]. The purple line is the [[celestial equator]], the projection of Earth's [[equator]] onto the [[celestial sphere]]. The [[Intersection (Euclidean geometry)|point]] (red) where these two lines cross is the [[March equinox|vernal equinox]]. In 1500 BCE, it was near the end of [[Aries (constellation)|Aries]]; in 500 BCE, it was near the beginning of Aries; and in 1000 to 2500 CE [[Pisces (constellation)|Pisces]].]]

==Astronomic zodiac==
{{main|Ecliptic|Zodiac}}
[[File:IAU Constellations with Traditional (Tropical) Zodiac Signs Overlaid.svg|thumb|A map of the [[International Astronomical Union|IAU]]-defined constellation boundaries with the equal length signs used in tropical astrology overlaid. One can see that, due to precession and the inequality in the sizes of constellations, it appears that the constellations the signs are based on have moved eastward by nearly a month (or 30 degrees). For example, the sign of Cancer mostly corresponds to the constellation Gemini.]]
Sidereal astrology does not divide the astrological signs equally along the ecliptic, unlike tropical astrology. But defines the signs based on the actual width of the individual constellations. Sidereal astrology also includes 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 astrology|tropical]] and sidereal dates are given as well.

{{sidereal and tropical zodiac dates}}

==See also==
* [[Great year]]
* [[Astrology and science]]
* [[Synoptical astrology]]

==References==
{{reflist|25em}}
{{sfn whitelist|CITEREFSchmidt1970}} <!-- for template:sidereal and tropical zodiac dates-->
{{refbegin|25em|small=yes}}
* {{cite book
 |last1=Fagan     |first1=Cyril
 |last2=Firebrace |first2=R.C., Brigadier
 |year=1971
 |title=The Primer of Sidereal Astrology
 |publisher=[[American Federation of Astrologers]]
 |place=Tempe, AZ
 |ISBN=0-86690-427-1
}}
* {{cite periodical
 |last=Mosley   |first=John
 |date=December 1999
 |title=The ''real'', real constellations of the zodiac
 |periodical=Planetarian
 |volume=28  |number=4  |pages=
 |url=http://www.ips-planetarium.org/planetarian/articles/realrealconstellations.html
 |via=ips-planetarium.org |url-status=dead <!-- presumed -->
 |archive-url=https://web.archive.org/web/20110427065257/http://www.ips-planetarium.org/planetarian/articles/realrealconstellations.html
 |archive-date=2011-04-27 |df=dmy
}}
* {{cite periodical
 |first=Lee T., Dr. |last=Shapiro
 |date=Spring 1977
 |title=The real constellations of the zodiac
 |periodical=Planetarian
 |volume=6  |number=1  |pages=
 |url=http://www.ips-planetarium.org/planetarian/articles/realconstellations_zodiac.html
 |via=ips-planetarium.org  |url-status=dead <!-- presumed --> 
 |archive-url=https://web.archive.org/web/20110126062745/http://www.ips-planetarium.org/planetarian/articles/realconstellations_zodiac.html
 |archive-date=2011-01-26 |df=dmy
}}
* {{cite book
 |last=Raymond |first=Andrew
 |year=1995
 |title=Secrets of the Sphinx: Mysteries of the ages revealed
 |publisher=U.N.I. Productions
 |location=Hawaii, US
 |isbn=0-9646954-6-4
 |url=https://books.google.com/books?id=JwAtAAAACAAJ  |via=Google books
}}
* {{cite book
 |first=S. Jim |last=Tester
 |year=1999 |orig-year=1987
 |title=A History of Western Astrology  |edition=reprint
 |publisher=Boydell Press
 |isbn=978-0-85115-255-4
}} {{ISBN|0-85115-255-4}}
{{refend}}

==External links==
*[http://www.astro.com/astrology/in_vedic2_e.htm Vedic astrology -- critically examined] by [[Dieter Koch]], with an extended discussion of sidereal and tropical astrology.

{{Jyotish Vidya}}
{{Chronology}}
{{Time Topics}}
{{Time measurement and standards}}

{{DEFAULTSORT:Sidereal Astrology}}
[[Category:Astrology by type]]
[[Category:Hindu astrology]]
[[Category:History of astrology]]
[[Category:Spring equinox]]