Showing posts with label surya siddhant. Show all posts
Showing posts with label surya siddhant. Show all posts

Sunday, November 4, 2018

Varahamihir, who predicted water in Mars


Even thousands of years before, India had become famous and reached its pinnacle in astrological and astronomical sciences. Ancient Astrological works had been translated into many foreign languages. Ibn Batuta and Al Baruni were two prominent Arab travelers who had visited ancient India specially to pursue Astrology. By their translations, they had induced German scholars to come to India to study Astrology and Vedic literature. Varahamihira was one of the only renowned Indian Astronomer, Mathematician and Astrologer whose name became a household word throughout India and it is said his near contemporaries Aryabhata and Brahmagupta even did not match with the popularity of Varahamihira.
Varahamihira was born in 505 A.D. into a family of Brahmins settled at Kapittha, a village near Ujjain. His father, Adityadasa was a worshipper of the Sun god and it was he who taught Varahamihira astrology. On a visit to Kusumapura (Patna) young Varahamihira met the great astronomer and mathematician, Aryabhata. The meeting inspired him so much the he decided to take up astrology and astronomy as a lifetime pursuit.
At that time, Ujjain was the center of learning, where many schools of arts, science and culture were flourishing in the prosperity of the Gupta reign. Varahamihira, therefore, shifted to this city, where scholars from distant lands were gathering. In due course, his astrological skills came to the notice of King Yashodharman Vikramaditya of Malwa, who made him one of the Nine Gems of his court.
Varahamihira was learned in the Vedas, but he was not a blind believer in the supernatural. He was a scientist. Like Aryabhata before him, he declared that the earth was spherical.
In the history of science, he was the first to claim that some “force” might be keeping bodies stuck to the round earth. The force is now called gravity. He proposed that the Moon and planets are lustrous not because of their own light but due to sunlight.
Varahamihira’s main work is the book Pancha Siddhantika (Treatise on the five Astronomical Canons gives us information about older Indian texts which are now lost). The work it seems is a treatise on mathematical astronomy and it summarises five earlier astronomical treatises, namely, the Surya Siddhanta, Romaka Siddhanta, Paulisa Siddhanta, Vasishtha Siddhanta, and Paitama Siddhanta.
It is acclaimed that Pancha Siddhantika of Varahamihira is one of the most important sources for the history of Hindu Astronomy from before the time of Aryabhata.
Another important contribution of Varahamihira is the encyclopedic Brihat-Samhita. It covers wide-ranging subjects of human interest, including astrology, planetary movements, eclipses, rainfall, rainfall, clouds even domestic relations, gems, pearls, and rituals.
Varahamihira in 550 AD has described a large number of comets in the Brhat Samhita. He wrote over sixty couplets about comets. He did not have the modern facilities like Telescope or other electronic equipment. He says that sages Garga, Parasara, Asita, Devala and others had already written about the comets.
He was also an astrologer and has written on all the three branches of astrology. His son Prithuyasas has also contributed in the Hindu astrology through his work, Hora Sara.
Varahamihira’s mathematical work included the discovery of the trigonometric formulas. He improved the accuracy of the sine tables of Aryabhata l. He defined the algebraic properties of zero as well as of negative numbers. Furthermore, He was among the first mathematicians to discover a version of what is now known as the Pascal’s triangle. He used it to calculate the binomial coefficients.
Varahamihira made some significant observations in the field of ecology, hydrology and geology too. He was the first person who predicted underground water. His claim that plants and termites serve as indicators of underground water is now receiving attention in the scientific world.
Varahamihira, without any scientific equipment, derived the true value of equinox. This value is very important for the modern-day Geostationary Satellites.

Surya Siddhanta & description on planet Mars:

  • Pancha siddhantika includes Surya Siddhanta, an astronomical treatise which explains or determines the true motions of the luminaries. Under this work, Varahamihira has also explained the estimated diameters of the planets, like Mercury, Venus, Mars, Saturn and Jupiter.
  • The book gave the locations of several stars other than the lunar nakshatras (constellations) and the calculation of solar eclipses. The book also had a significant coverage on kinds of time, the length of the year of gods and demons, day and night of god Brahma, the elapsed period since creation, how planets move eastwards and sidereal revolution.
  • Surya Siddhanta mentioned the Mars’s diameter (which was calculated to be 3,772 miles that has an error within 11% of the currently accepted diameter of 4,218 miles), circumference and also carries calculations on and about solar eclipses and lunar eclipses, its color and portion of the moon as well.
  • Apart from these, Varahamihira also predicted the presence of water on Mars. The book had a detailed description of planet Mars. He had said in his book that planet Mars has both water and iron present on its surface, which have now been revealed by NASA and ISRO.
  • He was the first to mention and explain how each planet in the solar system has been created by and centered on the sun.
It’s intriguing to know that during NASA’s Mars mission, Arun Upadhyay, a retired IPS, did a comparative study of Varāhamihira’s calculations about Mars and found certain similarities.
Though the original book of Surya Siddhanta till date remains untraced, but somehow a few scholars had taken their notes for their own research work. Many fear that the original version was stolen by the other astronomers from overseas. The present version of Surya Siddhanta, which is often used by Panchang experts to predict festive dates and nakshatras, was modified by Bhaskaracharya during the Middle Ages.
It is learnt, Varahamihira humbly said about his own treatises: “The science of Astrology is a vast ocean and is not easy for everyone to cross it. My treatises provide a safe boat.”  Truly, even now they are acknowledged as masterpieces.

Wednesday, May 27, 2015

Suryasiddhānta

In the chapter “Direction, Place and Time” (Suryasiddhānta, Ch.iii), E Burgess writes:
“(bracketed words are mine) : The (Surya Siddhāntic) theory which the passage (verses 9-12), in its present form, is actually intended to put forth is as follows : the vernal equinox librates westward and eastward from the fixed point, war Piscium, assumed as the commencement of the sidereal sphere– the limits of the libratory movement being 27 degrees in either direction from that point, and the time of a complete revolution of libration being the six-hundredth part of the period called the Great Age (ie, Mahāyuga as defined by Burgess in chapter i,15-17, where he gave it a span of 4320000 years), or 7200 years; so that the annual rate of motion of the equinox is 54″.”

This is the interpretation of existing version of Surya Siddhānta ( त्रिंशत्कृत्यो युगे भानां चक्रे प्राक् परिलम्बते …, SS,iii.9) in own words of E. Burgess , “as it is actually intended to put forth” by all traditional commentators. This is exactly what I illustrated with example in the illustrated example of computation of ayanamsha.
The moot point is this : Burgess knew the traditional interpretation (भानां चक्रे.., ie pendulum like motion of nakshatra orbit itself) , but gave his own meaning based upon modern concept of precession of equinoxes , and tried to create doubts about the authenticity of these verses (iii, 9-12) by putting forth deliberately false arguments. Let us examine Burgess.
In verse-9 (Suryasiddhānta, Ch.iii), he translates “pari-lambate” as “falls back”, although he says lambate means “lag, hang back, fall behind” and ‘pari’ means “about, round about”. Therefore, pari-lambate should have been translated as “fall back roundabout” and not merely as “fall back” according to own logic of Burgess. If the circle of asterisms lags roundabout any fixed point (whether Revati or Chitrā), it is a to and fro motion as all traditional commentators accepted. Modern concept of precession is something different from the original concept of ayanāmsha. Theon in West had mentioned this oscillating motion, Arab astronomers also accepted it, and almost all Europeans accepted it upto Renaissance, after which Hipparchus was rediscovered and modern concept of precession became a well established fact in astronomy. But this concept of equinoctial precession (as well as anomalistic precession) was also known to ancient Indians and Greeks.
Burgess wrongly quotes Bhāskara-II, because he relied upon a wrong translation of Bhāskara by Colebrooke (As. Res., xii 209 ; Essays, ii,374, etc) and did not try to examine Siddhānta Shiromani which was wrongly translated by Lancelot Wilkinson due to Colebrooke’s influence. Bhāskara-II did not give his own opinion at all, and merely quoted Surya Siddhānta and Mujjāl (elsewhere Munjāla and Manjula), saying Suryasiddhānta gives -30000 revolutions of sampāt or equinoctial point per Kalpa while ayana has a motion of +199669 revolutions per Kalpa (of 4320 million years). Bhāskara’s own opinion was that these should be followed, which means both Surya Siddhānta and Mujjāla were correct in Bhāskara’s opinion. Colebrooke, Burgess, Wilkinson, etc have misquoted Siddhānta Shiromani and created an impression that ancient Indians were inept in astronomical observations, as Whitney shamelessly declared in his prologue to Burgess, but the Hindi translation by Satyadeva Sharmā is correct, although he could not get the real meaning.
The startling fact is that Siddhānta Shiromani clearly says that “the point of intersection of equatorial plane and ecliptic” (which is the very definition of equinox) has a negative motion of 30000 revolutions per Kalpa according to Suryasiddhānta, while Mujjala’s value of ayana’s motion is +199669, and both (Suryasiddhānta and Mujjala ) must be added to get the final motion (of the equinox ). Hence, we get +169669 revolutions per Kalpa, which gives (4320000000 / 169669 =) 25461 years per revolution or 50.9″ per year, which is very near to modern value of about 50.3″ per year for precession of equinoxes.
We must not forget that Hipparchus had given a period of 36000 years for precession, which was not corrected by Europeans till the onset of modern age. It is unfortunate that Siddhānta Shiromani is still being misinterpreted by foreigners, and if a true rendering is offered by Indian scholars, they are abused, esp by those who do not care to consult the originals and declare the forign missionaries to reliable. Bhāskara-II neither excluded Suryasiddhānta, nor Mujjāla, but mentioned the both must be used, which is clear from verse-19, where he clearly asks to add Mujjāla’s ayana-chalam to Suryasiddhāntic sampāt-chalanam (this sampāt-chalanam is anomalistic precession with a period of 144000 years per cycle, against modern value of 136000 years).
Another startling fact is that Bhāskara-ii differentiates sampāt-chalanam of Suryasiddhānta from ayana-chalanam of Mujjāla, and says both must be added before computing phenomena like declension, ascensional differences, etc. But modern commentators like Colebrooke misinterpret Bhāskara-II deliberately, and imply that sampāt-chalanam of Suryasiddhānta quoted by Bhāskara-ii was an erroneous thing which must be forgotten, while ayana-chalanam of Mujjāla was a crude approximation of modern precession. But this interpretation is falsified by Bhāskara’s original verses as shown above. The root of this problem lies in the fact that sampāt-chalanam of Suryasiddhānta is a distinct phenomenon from ayana-chalanam of Mujjāla according to Siddhānta Shiromani, but readers are not informed of the real meaning of Siddhānta Shiromani and false quotation from Siddhānta Shiromani was quoted by Colebrooke and Burgess (12th verse, chap.iii). This is a sign of intellectual incompetence and dishonesty of Western “experts” who are blindly followed by brown sāhibs of India. Those who do not consult the original texts cited above will not believe me.
Siddhānta-tattva-viveka by Kamlākara Bhatt is a medieval text, which clearly states that Saurpaksha is distinct from Drikpaksha. Saurpaksha (astronomy of bhuvaloka) is Suryasiddhānta as it exists. Drikpaksha (astronomy of Bhooloka or physical/material/sensory world) is that version of Suryasiddhānta which was not preserved because it was useless in astrology. Siddhānta Shiromani uses many concepts of Drikpakshiya astronomy, as the instance cited above proves. Saurpakshiya Suryasiddhānta does not contain any refence to 30000 cylces per Kalpa mentioned by Bhāskara-II. He was quoting from Drikpakshiya Suryasiddhānta which as a text had been lost ; Bhāskara-II said in his own Vāsanābhāshya commentary of Siddhānta-shiromani that Suryasiddhānta is not available (“anupalabdha”) and he was quoting it on the basis of “āgama”. Only its fragments are left, scattered here and there. Modern commentators confuse both variants of Suryasiddhānta. Siddhāntatattvaviveka is prescribed in post-graduate (Ganitāchārya) syllabus of Sanskrit universities, but no modern commentator has ever tried to translate it or comment on it.
According to Bhāskara-ii , negative sampāt-chalanam of Drikpakshiya Suryasiddhānta should be added to positive ayana-chalanam of Mujjāla to get final Drikpakshiya precession, which is very close to modern value. Ayana-chalanam of Mujjāla is also Drikpakshiya, because Saurpakshiya entities are not used in Drikpakshiya astronomy, and vice versa. I have put some of the most important extant theorems of Drikpakshiya Suryasiddhānta at a website. I had put parts of it at one of most popular websites, where a German “Indologist” deleted it and abused me profusely ; later I found those deleted materials at an Australian website, without any name of author!!. But I am here divulging one important secret of ancient science of India which has been neglected by wrongheaded commentators.
Mujjāla’s ayana-chalanam, as mentioned in Siddhānta Shiromani, gives a period of (4320 million / 199669 = ) 21636 years per cycle. Siddhānta Shiromani says that it is ayanachalanam and not precession, precession is obtained after substracting (Saurpakshiya) Suryasiddhāntic sampātchalanam. If this 21636 year cycle is not precession, what is it ??
Readers should read a Wikipedian article Milankovitch cycles ( http://en.wikipedia….lankovic_cycles ) which informs :”Earth’s axis completes one full cycle of precession approximately every 26,000 years (25771.5 precisely at present, 25789.5 years is long term mean). At the same time, the elliptical orbit rotates, more slowly, leading to a 21,000-year cycle between the seasons and the orbit… This orbital precession is in the opposite sense to the gyroscopic motion of the axis of rotation(cf. anomalistic precession as distinct from equinoctial precession), shortening the period of the precession of the equinoxes with respect to the perihelion from 26,000 to 21,000 years.” (at some sites of NOAA of USA, 22000 is mentioned instead of 21000)
Ayana-chalanam of Mujjāla is not orbital precession, it is the most important of all components of Milankovitch cycles as this Wikipedian definition shown. If we take cue from Siddhānta Shiromani, the aforementioned Wikipedian clause can be rewritten thus : This orbital precession of equinoxes is in the opposite sense to the gyroscopic motion of the axis of rotation, shortening the period of the precession of the equinoxes with respect to the perihelion from 25771 to 21,636 years.
Siddhānta Shiromani also says that Mujjāla’s ayana-chalanam (21,636 years per cycle) is opposite to sampāta-chalanam. Bhāskara-ii clearly defines sampāta-chalanam as “the point of intersection of equatorial plane and ecliptic” (which is the very definition of equinox). Hence, what Siddhānta Shiromani says is exactly what Wikipedia informs us, the only difference is that Siddhānta Shiromani is misinterpreted and declared to be obscurantist, and the great cycles mentioned in Siddhānta Shiromani is “discovered” by 20th century scientists. But we must remember Bhāskara-ii did not discover these things, he acknowledged Suryasiddhānta and Munjāla.
Bhāskara-ii knew Drikpakshiya Suryasiddhānta, which has not survived because it was not useful in astrology. In his formula of precession, Bhāskara-II used a figure 30000 cycles per Kalpa. Bhaskara-II got an approximate value of 50.9″ per year, which was the most precise value before modern astronomy developed in the West. Here I quote a Puranic verse which proves knowledge of equinoctial precession in Puranic times :
उत्तानपादपुत्रोऽसौ मेढीभूतो ध्रुवो दिवि ।
स हि भ्रमन् भ्रामयते नित्यं चन्द्रादित्यौ ग्रहैः सह ।।
It means : “Uttanpāda’s son Dhruva is the fixed point in the Heavens , round which all planets including Sun and Moon, but Dhruva himself also moves round” . Round what ? Mt Meru, which is the only fixed point in Cosmos according to Purānic-epic stories. Hence, the bhachakra also librates with respect to this fixed point Meru.
According to Bhāskara-II, orbital precession is derived by substracting anomalistic precession (sampāt-chalanam) from the first component of Milankovitch cycles (Munjāla’s ayana-chalanam). Bhāskara-II acknowledged earlier authors. Hence, we must conclude that modern values and concepts of orbital precession, anomalistic precession, Milankovitch cycles, etc were known to ancient Indians well before Bhāskara-ii.
But two things about confusing terminology must be borne in mind : this sampāt-chalanam he finally gets by combining the two quantities mentioned above. According to Bhāskara-II, Suryasiddhāntic sampāt-chalanam is 30000 per Kalpa. He does not give a name for the term which is finally obtained by combining this sampāt-chalanam with Munjāla’s ayana-chalanam, but the definition he provides for Suryasiddhāntic sampāt-chalanam is exactly the definition of the final quantity whose name he does not provide. Hence, there were many types of sampāt-chalanams !! This is not a case of confusion of terms. It is a result of Saurpakshiya term with Drikpakshiya terms bearing same names but having different magnitudes and sometimes even having difference in basic properties !
Second confusion is due to use of the term ayana-chalanam for Munjāla’s precession. It is quite distinct from Saurpakshiya Suryasiddhāntic ayana-chalanam (trepidation) as mentioned in existing text. Burgess could not digest this theory of libration (oscillation or trepidation, ie, ayanāamsha – motion) and tried to distort the meaning of terms to fit modern view of orbital precession with this Saurpakshiya precession. Bhāskara-ii knew and respected Suryasiddhānta which he cited and used in his computations as shown above, and gave exact value of Drikpakshiya precession. Therefore, it is foolish to impose Drikpakshiya precession (50.9″ per year according to Bhāskara-II, 50.3″ really) upon Saurpakshiya ayanamsha (54″ per year, oscillating within a range of ± 27 degrees). (There are further corrections on Drikpakshiya precession which give a final value of one revolution in 25771.4 years, exactly equal to the value deduced by NASA – JPL , but these corrections requires some long theorems to prove).
I do not want to say that all ancient texts are true and should be blindly followed. But it is equally wrong to deride them as outdated and obscurantist just because they could not be understood by moderns.We have yet to discover the real Wonder that Is India. Unless and until ancient texts are proven false, it is suicidal to reject them.

Sunday, March 29, 2015

Surya Siddhanta, >2 Million Years old Book is First on Astronomy

Image result for surya siddhantaImage result for surya siddhantaSurya Siddhanta is the first among the traditions or doctrines (siddhanta) in archaeo-astronomy of the Vedic era.
Infact, it is the oldest ever book in world which describes earth as sphere but not flat, gravity being reason for objects falling on earth etc.
This is the knowledge that the Sun god gave to an Asura called Maya in Treta Yuga.
This Maya is father-in-law of Ravana, the villain of first ever epic poem, Ramayana.
Going by calculations of Yugas, first version ofSurya Siddhanta must have been known around 2 million years ago.
However, the present version available is believed to be more than 2500 years old, which still makes it the oldest book on earth in Astronomy.
This book covers kinds of time, length of the year of gods and demons, day and night of god Brahma, the elapsed period since creation, how planets move eastwards and sidereal revolution. The lengths of the Earth’s diameter, circumference are also given. Eclipses and color of the eclipsed portion of the moon is mentioned.
This explains the archeo-astronomical basis for the sequence of days of the week named after the Sun, Moon, etc. Musings that there is no above and below and that movement of the starry sphere is left to right for Asuras (demons) makes interesting reading.
Citation of the Surya Siddhanta is also found in the works of Aryabhata.
The work as preserved and edited by Burgess (1860) dates to the Middle Ages.
Utpala, a 10th-century commentator of Varahamihira, quotes six shlokas of the Surya Siddhanta of his day, not one of which is to be found in the text now known as the Surya Siddhanta. The present version was modified by Bhaskaracharya during the Middle Ages.
The present Surya Siddhanta may nevertheless be considered a direct descendant of the text available to Varahamihira (who lived between 505–587 CE)
Table of contents in Surya Siddhanta are :-
  • The Mean Motions of the Planets
  • True Places of the Planets
  • Direction, Place and Time
  • The Moon and Eclipses
  • The Sun and Eclipses
  • The Projection of Eclipses
  • Planetary Conjunctions
  • Of the Stars
  • Risings and Settings
  • The Moon’s Risings and Settings
  • Certain Malignant Aspects of the Sun and Moon
  • Cosmogony, Geography, and Dimensions of the Creation
  • The Gnomon
  • The Movement of the Heavens and Human Activity
Methods for accurately calculating the shadow cast by a gnomon are discussed in both Chapters 3 and 13.

Few excerpts from Surya Siddhanta

  • The average length of the tropical year as 365.2421756 days, which is only 1.4 seconds shorter than the modern value of 365.2421904 days !
  • The average length of the sidereal year, the actual length of the Earth’s revolution around the Sun, as 365.2563627 days, which is virtually the same as the modern value of 365.25636305 days. This remained the most accurate estimate for the length of the sidereal year anywhere in the world for over a thousand years!
  • Not content to limit measurements to Earth, the Surya Siddhanta also states the motion, and diameters of the planets! For instance the estimate for the diameter of Mercury is 3,008 miles, an error of less than 1% from the currently accepted diameter of 3,032 miles. It also estimates the diameter of Saturn as 73,882 miles, which again has an error of less than 1% from the currently accepted diameter of 74,580.
  • Aside from inventing the decimal system, zero and standard notation (giving the ancient Indians the ability to calculate trillions when the rest of the world struggled with 120) the Surya Siddhanta also contains the roots of Trigonometry.
  • It uses sine (jya), cosine (kojya or “perpendicular sine”) and inverse sine (otkram jya) for the first time!
  • Objects fall on earth due to a force of attraction by the earth. therefore, the earth, the planets, constellations, the moon and the sun are held in orbit due to this attraction”. (this was also discussed in Prasnopanishad
    It was not until the late 17th century in 1687, that Isaac Newton rediscovered the Law of Gravity.
  • The Surya Siddhanta also goes into a detailed discussion about time cycles and that time flows differently in differently circumstances, the roots of relativity. Here we have a perfect example of Indian philosophy’s belief that science and religion are not mutually exclusive. Unlike, Abrahamic religions, one does not have to dig and try all ways to force scientific truth from scriptures. By contrast it is stated in cold hard numbers by the Sun God, Surya.
  • This work shows that spirituality is all about the search for Truth (Satya) and that Science is as valid a path to God as living in a monastery. It is the search for ones own personal Truth that will lead one ultimately to God.
The astronomical time cycles contained in the text were remarkably accurate at the time.
  • That which begins with respirations (prana) is called real…. Six respirations make a vinadi, sixty of these a nadi
  • And sixty nadis make a sidereal day and night. Of thirty of these sidereal days is composed a month; a civil (savana) month consists of as many sunrises
  • A lunar month, of as many lunar days (tithi); a solar (saura) month is determined by the entrance of the sun into a sign of the zodiac; twelve months make a year. This is called a day of the gods. (Day at North Pole)
  • The day and night of the gods and of the demons are mutually opposed to one another. Six times sixty of them are a year of the gods, and likewise of the demons. (Day and Night being six months each at South Pole)
  • Twelve thousand of these divine years are denominated a chaturyuga; of ten thousand times four hundred and thirty-two solar years
  • Is composed that chaturyuga, with its dawn and twilight. The difference of the kritayuga and the other yugas, as measured by the difference in the number of the feet of Virtue in each, is as follows:
    a. The tenth part of a chaturyuga, multiplied successively by four, three, two, and one, gives the length of the krita and the other yugas: the sixth part of each belongs to its dawn and twilight.
    b. One and seventy chaturyugas make a manu; at its end is a twilight which has the number of years of a kritayuga, and which is a deluge.
    c. In a kalpa are reckoned fourteen manus with their respective twilights; at the commencement of the kalpa is a fifteenth dawn, having the length of a kritayuga.
    d. The kalpa, thus composed of a thousand chaturyugas, and which brings about the destruction of all that exists, is a day of Brahma; his night is of the same length.
    e. His extreme age is a hundred, according to this valuation of a day and a night. The half of his life is past; of the remainder, this is the first kalpa.
    f. And of this kalpa, six manus are past, with their respective twilights; and of the Manu son of Vivasvant, twenty-seven chaturyugas are past;
    g. Of the present, the twenty-eighth, chaturyuga, this kritayuga is past..

Planetary Diameters in Surya Siddhanta

Surya Siddhanta also estimates the diameters of the planets. The estimate for the diameter of Mercury is 3,008 miles, an error of less than 1% from the currently accepted diameter of 3,032 miles.
It also estimates the diameter of Saturn as 73,882 miles, which again has an error of less than 1% from the currently accepted diameter of 74,580.
Its estimate for the diameter of Mars is 3,772 miles, which has an error within 11% of the currently accepted diameter of 4,218 miles.
It also estimated the diameter of Venus as 4,011 miles and Jupiter as 41,624 miles, which are roughly half the currently accepted values, 7,523 miles and 88,748 miles, respectively.

Trigonometry in Surya Siddhanta

Surya Siddhanta contains the roots of modern trigonometry. It uses sine (jya), cosine (kojya or “perpendicular sine”) and inverse sine (otkram jya) for the first time, and also contains the earliest use of the tangent and secant when discussing the shadow cast by a gnomon in verses 21–22 of Chapter 3:
Of [the sun’s meridian zenith distance] find the jya (“base sine”) and kojya (cosine or “perpendicular sine”). If then the jya and radius be multiplied respectively by the measure of the gnomon in digits, and divided by the kojya, the results are the shadow and hypotenuse at mid-day.
In modern notation, this gives the shadow of the gnomon at midday as :
trignometry in surya siddhanta
Even today many astrologers in India use Surya Siddhanta as base to compute their Panchangs (Almanacs) in many languages.
citation- Booksfact.com