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'''''Sūrya Siddhānta''''' is an ancient Indian treatise in Astronomy. Like many classical Indian works, the ''Sūrya Siddhānta'' is a poem in [[Sanskrit]] language. It has fourteen chapter and 500 verses. It is composed in ''śloka'' metrical style of Sanskrit. It contain works on Indian sine tables, cosmology, eclipses, planetary motions, conjunctions, star positions, geography, instrumentation, concepts of time and mathematics. Unlike conventional books ''Sūrya Siddhānta'' contains advanced calculation and methods which are not easily comprehensible for a rank beginner. <ref>[https://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol45_4_1_ANarayan.pdf]</ref> In second chapter, the text contains the calculation of Earth's obliquity of ''1397 jya (R.sine) 23.975°'' modern units. The text describes the observation of two pole stars one each at the north pole and the south pole seen at the equatorial region, such phenomena was last seen in the 3rd millennium BCE. This indicates the antiquity of the concepts recorded in the text.<seo title="Surya Siddhanta" titlemode="append" keywords="Surya Siddhanta, surya, Surya Siddhanta dharma, dhammawiki" description="Sūrya Siddhānta is an ancient Indian treatise in Astronomy. Like many classical Indian works, the Sūrya Siddhānta is a poem in Sanskrit language. It has fourteen chapter and 500 verses. It is composed in śloka metrical style of Sanskrit. It contain works on Indian sine tables, cosmology, eclipses, planetary motions, conjunctions, star positions, geography, instrumentation, concepts of time and mathematics."></seo>

'''''Sūrya Siddhānta''''' is an ancient Indian treatise in Astronomy. Like many classical Indian works, the ''Sūrya Siddhānta'' is a poem in [[Sanskrit]] language. It has fourteen chapter and 500 verses. It is composed in ''śloka'' metrical style of Sanskrit. It contain works on Indian sine tables, cosmology, eclipses, planetary motions, conjunctions, star positions, geography, instrumentation, concepts of time and mathematics. Unlike conventional books ''Sūrya Siddhānta'' contains advanced calculation and methods which are not easily comprehensible for a rank beginner. <ref>[https://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol45_4_1_ANarayan.pdf]</ref> The text had been updated several times and the last update appears to have  been made around 580 CE to the ''Nakshatra'' longitudes. In second chapter, the text contains the calculation of Earth's obliquity of ''1397 jya (R.sine) 23.975°'' modern units indicating the time of calculation around 3000 BCE. There are several other observations in the tradition of ''Indian Astronomy'' that were also recorded in the vicinity of 3000 BCE. This could possibly be the time of the origin of ''Sūrya Siddhānta'' although scholars do not seem to have a consensus on the origin of this text of ''Indian Astronomy''.

 

== History ==

== History ==

<nowiki>''Sūrya Siddhānta'' is well known, most referred and most esteemed. The original author of ''Sūrya Siddhānta'' is ''Mayasura'' as described in the story in the first chapter that ''Mayasura'' obtained his knowledge from ''Sūrya'' (the Sun). ''Siddhānta'' in Sanskrit means ''treatise'' and it usually has author'</nowiki>s name prefixed to it. There were several other works on Astronomy in ancient India, many of which have since been lost.

<nowiki>''Sūrya Siddhānta'' is well known, most referred and most esteemed. The original author of ''Sūrya Siddhānta'' is ''Mayasura'' as described in the story in the first chapter that ''Mayasura'' obtained his knowledge from ''Sūrya'' (the Sun). ''Siddhānta'' in Sanskrit means ''treatise'' and it usually has author'</nowiki>s name prefixed to it. There were several other works on Astronomy in ancient India, many of which have since been lost.

The ''Surya Siddhanta'' uses the 27 [[Nakshatra system]] throughout the text. The Nakshatra is a smaller constellation typically consisting of 1 to 5 stars. The brightest star is called as Yogtara. Each Nakshatra spans 13° 20' on the ecliptic. Each Nakshatra has its own primary star which is usually the junction star but not always.

The ''Surya Siddhanta'' uses the 27 [[Nakshatra system]] throughout the text. The Nakshatra is a smaller constellation typically consisting of 1 to 5 stars. The brightest star is called as Yogtara. Each Nakshatra spans 13° 20' on the ecliptic. Each Nakshatra has its own primary star which is usually the junction star but not always.

=== Longitudinal updates - 580 AD ===

=== Longitudinal updates ===

Chapter 8 of ''Surya Siddhanta'' primarily focuses on the stellar data. It provides the longitudinal data for the Asterisms. In comparison to the present day longitudinal values of these stars and the data of Surya Siddhanta, it becomes clear that this update to Surya Siddhanta was made around 580 AD. THe longitude of the stars change by 1° in every 71 years. From the data it is clear that the data does not represent observation but rather is obtained by adding precessional increment to each of the previously calculated data.

Chapter 8 of ''Surya Siddhanta'' primarily focuses on the stellar data. It provides the longitudinal data for the Asterisms. In comparison to the present day longitudinal values of these stars and the data of Surya Siddhanta, it becomes clear that this update to Surya Siddhanta was made around 580 AD. THe longitude of the stars change by 1° in every 71 years. From the data it is clear that the data does not represent observation but rather is obtained by adding precessional increment to each of the previously calculated data.

=== Obliquity (tilt) of the Earth's axis - 3000 BC ===

=== Obliquity (tilt) of the Earth's axis ===

Obliquity or the axial tilt of earth is the angle which the earth's axis of rotation makes with the perpendicular of orbital plane. This angle varies between 22.1° and 24.5° and it is cyclic phenomena over a period of 41,000 years. Currently the obliquity is 23.4 degrees.<ref>Alan Buis, "Milankovitch (Orbital) Cycles and Their Role in Earth's Climate", "NASA's Jet Propulsion Laboratory" https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/</ref> ''Sūrya Siddhānta'' in two different chapters calculate and provide the value of obliquity.

Obliquity or the axial tilt of earth is the angle which the earth's axis of rotation makes with the perpendicular of orbital plane. This angle varies between 22.1° and 24.5° and it is cyclic phenomena over a period of 41,000 years. Currently the obliquity is 23.4 degrees.<ref>Alan Buis, "Milankovitch (Orbital) Cycles and Their Role in Earth's Climate", "NASA's Jet Propulsion Laboratory" https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/</ref> ''Sūrya Siddhānta'' in two different chapters calculate and provide the value of obliquity.

{{Quote  

{{Quote  

|text = ''The sine of the greatest declination is 1397 units; Multiply the sine by the said sine 1397; Divide the product by the radius 3438 units; Find the arc whose sine is equal to the quotient. This arc is the mean declination of the planet''<ref>E. Burgess, "Translation of Surya Siddhanta", p26, Accessible at https://www.jstor.org/stable/pdf/592174.pdf</ref>

|text = ''The sine of the greatest declination is 1397 units; Multiply the sine by the said sine 1397; Divide the product by the radius 3438 units; Find the arc whose sine is equal to the quotient. This arc is the mean declination of the planet''<ref>E. Burgess, "Translation of Surya Siddhanta", p26, Accessible at https://www.jstor.org/stable/pdf/592174.pdf</ref>

}} This way we obtain the obliquity as Sin^-1(1397/3438) = 23.975°

}}

This way we obtain the obliquity as Sin^-1(1397/3438) = 23.975°

{{Quote  

{{Quote  

|text = ''At the distance of the fifteenth part of the Earth's circumference (from the equator) in the regions of the Gods or the Asuras (i.e. at the north and south terrestrial tropic) the sun passes through the zenith when it arrives at the north or south solstitial point (respectively)''''<ref>Pundit Bapu Deva Shastri, "Translation of Surya Siddhanta", "Baptist Mission Press", 1861, Accessible at https://www.wilbourhall.org/pdfs/suryaEnglish.pdf</ref>

|text = ''At the distance of the fifteenth part of the Earth's circumference (from the equator) in the regions of the Gods or the Asuras (i.e. at the north and south terrestrial tropic) the sun passes through the zenith when it arrives at the north or south solstitial point (respectively)''''<ref>Pundit Bapu Deva Shastri, "Translation of Surya Siddhanta", "Baptist Mission Press", 1861, Accessible at https://www.wilbourhall.org/pdfs/suryaEnglish.pdf</ref>

}} It essentially provides information to calculate the axial tilt of earth which in this case can be calculated as 360°/15 = 24°.

}}

It essentially provides information to calculate the axial tilt of earth which in this case can be calculated as 360°/15 = 24°.

The significance of these verses is that they pin points the exact time when the obliquity calculations were made by ancient Indian astronomers and added into the ''Sūrya Siddhānta''. The epoch this obliquity calculation provides is around 3000BC.<ref>Anil Narayanan, "Dating the Surya Siddhanta using Computer simulation of Proper Motions and Ecliptic variations", ''Indian Journal of History of Science'', Volume 45, issue 4, 23 March 2010.</ref>

The significance of these verses is that they pin points the exact time when the obliquity calculations were made by ancient Indian astronomers and added into the ''Sūrya Siddhānta''.  

=== North Pole Star and South Pole Star - 3000 BC ===

=== North Pole Star and South Pole Star ===

''Surya Siddhanta'' contains an observation of the presence of pole stars at both north celestial pole and south celestial pole. Because of the precession of the earth's axis it is known that the pole star changes over a period of time which is normally more than thousand years. In present times our North Pole star is Polaris.<ref>Bruce McClure, "Polaris is the North Pole Star", "Earthsky", 21 May 2019, Accessible at https://earthsky.org/brightest-stars/polaris-the-present-day-north-star</ref> This observation is recorded in chapter 12, verse 43-44 and translates as  

''Surya Siddhanta'' contains an observation of the presence of pole stars at both north celestial pole and south celestial pole. Because of the precession of the earth's axis it is known that the pole star changes over a period of time which is normally more than thousand years. In present times our North Pole star is Polaris.<ref>Bruce McClure, "Polaris is the North Pole Star", "Earthsky", 21 May 2019, Accessible at https://earthsky.org/brightest-stars/polaris-the-present-day-north-star</ref> This observation is recorded in chapter 12, verse 43-44 and translates as  

{{Quote

{{Quote

}}

}}

Such phenomena was last seen around 3000 BC when Thuban was the North Pole Star and Alpha Hydri was the South Pole star.<ref>Nilesh N Oak and Rupa Bhatty, "Ancient Updates to Surya Siddhanta", 09 March 2019, "India Facts" Accessible at http://indiafacts.org/ancient-updates-to-surya-siddhanta/</ref> <ref> Anil Narayanan, "Wonders, Mysteries and Misconceptions in Indian Astronomy – I", 'India facts", 09 Sept 2019, Accessible at http://indiafacts.org/wonders-mysteries-and-misconceptions-in-indian-astronomy-i/</ref>

Such phenomena was last seen around 3rd millennium BCE when Thuban was the North Pole Star and Alpha Hydri was the South Pole star.<ref>Nilesh N Oak and Rupa Bhatty, "Ancient Updates to Surya Siddhanta", 09 March 2019, "India Facts" Accessible at http://indiafacts.org/ancient-updates-to-surya-siddhanta/</ref> <ref>Anil Narayanan, "Wonders, Mysteries and Misconceptions in Indian Astronomy – I", 'India facts", 09 Sept 2019, Accessible at http://indiafacts.org/wonders-mysteries-and-misconceptions-in-indian-astronomy-i/</ref> This indicates the antiquity of the concepts written in the text.

 

 

Using computer simulation of nakshatra latitudinal data by varying ecliptic obliquity, ecliptic-node-location and ecliptic-sink together with proper motion, a match for the Surya Siddhanta latitudinal data was obtained in the timeframe 7300-7800 BC.<ref>Anil Narayanan, "Dating the Surya Siddhanta using Computer simulation of Proper Motions and Ecliptic variations", ''Indian Journal of History of Science'', Volume 45, issue 4, p21, 23 March 2010.</ref> Although the author notes that a major assumption made in this investigation is that star proper motion is fairly constant over several thousands of years. The results may be adversely affected if this were found untrue for the star set under consideration. It should also be noted that this time frame matches with the establishment of the oldest archaeological site of Bhirrana found along the Saraswati river paleochannel. In the 8th millennium BC this site shows that the people were living in the dwelling pits.<ref>Bhirrana, "Archaeological Survey of India", http://excnagasi.in/excavation_bhirrana.html</ref> This stands in contrast with the above time frame, the question arises whether people could be that scientifically advanced while they were inhabiting the dwelling pits. Although this view is subject to change given older more advanced archaeological sites are found within the Indian subcontinent.

=== ''Surya Siddhanta'' sine table ===

=== ''Surya Siddhanta'' sine table ===