Surya Siddhanta — Part 2 of 2

Decoding the scientific findings

Following the glimpse into the colossal magnificence of this ancient wonder of Indian Astronomy, we shall now attempt decipher the nuances of the lapidary verses in this article.

Surya Siddhanta is enriched by the language and has ample scientific facts in the form of verses. The text asserts, according to Markanday and Srivatsava, that the earth is of a spherical shape. 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 metrics of the Earth’s diameter and circumference are also given. Eclipses and colour of the eclipsed portion of the moon is mentioned.

Given below highlights and interprets few slokas from the 14 chapters:

Chapter 12, verse 12.53 states that:

Thus everywhere on [the surface of] the terrestrial globe, people suppose their own place higher [than that of the others], yet this globe is in space where there is no one above or below.

Using that there is no above and below and that movement of the starry sphere is left to right for Asuras (demons) makes interesting reading. This indicates that ancient Indians had a considerable knowledge about outer space.

Chapter 12, verse 12.43 and 12.44, which provides stunning evidences for pole stars, is as follows

There are two pole stars, one each, near Northern Celestial point and near Southern Celestial point. From equatorial locations, these stars are seen along the horizon.

The pole stars are seen along the horizon, from these places, and thus the place latitude is close to zero, while the declination of Northern Celestial Pole and Southern Celestial Pole is 90 degrees.

Considering the age of the text, it’s worthy to note here that pole stars aren’t constant and vary over thousands of years. Researchers say that at around 1200BC (the time when Surya Siddhanta was probably scripted), there was indeed a Northern and Southern pole star, Canopus (Agastya) and Vega (Abhijit) respectively, contrary to Polaris (Northern pole star) and absence of Southern pole star.

Further, sloka 12:45 and 12:46 predicts periapsis and apoapsis and provides direct evidence to Kepler’s laws.

In the half revolution beginning with Aries, the Sun, being in the hemisphere of the gods, is visible to the gods: but while in that beginning with Libra, he is visible to the demons, moving in their hemisphere.

Hence, owing to these exceeding nearness, the rays of sun are hot in the hemisphere of gods in summer, but in that of the demons in winter: in the contrary season, they are sluggish

Verse 12.68 of Surya Siddhanta has stated that the inclination of Earth along its axis is 24 degrees, a value close enough to the modern revelations of 23.4366 degrees. But, astronomers do believe the value provided by Surya Siddhanta can actually state the fact that Earth’s obliquity oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle, considering the age of the sacred text.

The sun during his northern and southern progresses (ayana) revolves directly over a fifteenth part of the Earth’s circumference, on the side both of the gods and demons.

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 sloka shows that people at those times had formulated the presence of an invisible force (now called gravity) that is behind objects falling back on Earth.

For each planet, the orbital circumference is a constant multiple of its time period. This comes about because of the following rule in the Surya Siddhanta for computing the orbital circumferences:

If the stated number of revolutions of the moon in an Aeon (kalpa) be multiplied by the moon’s orbit, the result is to be known as the orbit of the ether: so far do the sun’s rays penetrate. [12.81]

If this be divided by the number of revolutions of any planet in an Aeon (kalpa), the result will be the orbit of that planet: divide this by the number of terrestrial days, and the result is the daily eastward motion of them all. [12.82]

The idea behind this rule is that all of the planets move at the same mean rate in their geocentric orbits. Since the Surya Siddhanta gives accurate figures for the revolutions of each planet in a kalpa, this rule results in orbital circumferences proportional to the modern geocentric periods of the planets. (According to modern astronomy, the period squared should be proportional to the orbital circumference cubed.)

The Surya Siddhanta says that there are 15 yojanas per minute of the arc at the distance of the moon. Thus, the mean angular diameters of the planets can be computed by dividing the diameters upon the moon’s orbit by 15. If we analyse the data transcribed about the angular diameters of various celestial bodies in Surya Siddhanta, we can find all the values on the higher side as juxtaposed to the modern era calculations. But, considering the fact that a small, distant light source looks larger to the naked eye than it really is, this shows that all the measurements were made by naked eye!

Surya Siddhanta follows a model based on precession of equinoxes. It makes use of the zodiac signs to make calculations on astronomical distances.

• The text asserts that the average length of the tropical year is 365.2421756 days, which is only 1.4 seconds shorter than the modern value of 365.2421904 days!
• Not content to limit measurements to Earth, the Surya Siddhanta also states the motion, and diameters of the planets too! 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 estimates the diameter of Saturn as 73,882 miles, which is just short by 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.
• The most fascinating revelation is the sidereal period of the moon as 27.322 , compared to 27.32166 in modern calculations. For Mercury it states the period to be 87.97 (modern result: 87.969), Venus as 224.7 (modern: 224.701), Mars as 687 (modern: 686.98), Jupiter as 4,332.3 (modern: 4,332.587) and Saturn to be 10,765.77 days (modern: 10,759.202).
• The Surya Siddhanta also goes into a detailed discussion about time cycles and that time flows differently in different circumstances, the roots of relativity. Here we have a perfect example of Indian philosophy’s belief that science and religion are not mutually exclusive.
• It has described rules to calculate the motions of various planets and the moon relative to various constellations, diameters of various planets, and the orbits of various astronomical bodies. The text asserts that the universe is of a spherical shape.

All the shlokas stand as an incredible testimony of the advanced thinking of the Ancient Indians.

One possible hypothesis is that at some time in the past, ancient astronomers possessed realistic values for the diameters of the planets. One can suppose that they might have acquired this knowledge during a forgotten period in which astronomy reached a high level of sophistication and planets were observed using telescopes or other advanced instruments. Later on, much of this knowledge was lost, but fragmentary remnants were preserved and eventually incorporated into texts such as the Surya Siddhanta.

Surya Siddhanta also explains about a myriad of mathematical concepts like Trigonometry functions and sexagesimal fractions.

It contains the roots of modern trigonometry. This is evident from the use of trigonometric ratios like 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.

The Surya Siddhanta is a text on astronomy and time keeping, an idea that appears much earlier as the field of Jyotisha (Vedanga) of the Vedic period. The field of Jyotisha deals with ascertaining time, particularly forecasting auspicious day and time for Vedic rituals.

The solar part of the luni-solar Hindu calendar is based on the Surya Siddhanta. The various old and new versions of Surya Siddhanta manuscripts yield the same solar calendar. Both the Hindu and Buddhist calendars used in South and Southeast Asia are rooted in this text, but the regional calendars have adapted and modified them over time.

“Panchang” (almanac) makers still use the formulae and equations found in the “Surya Siddhanta” to compile and compute their panchangas. It exerts great influence on the religious and the social life of people in India and is found in most Hindu households. On an average, according to the text, the lunar month equals 27 days 7 hours 39 minutes 12.63 seconds. It states that the lunar month varies over time, and this needs to be factored in for accurate time keeping.

The entire collection of Surya Siddhanta has well substantiated asseverations on scientific notions, a clear indication that Indians were at the forefront of moving towards the understanding of the reality that was hidden behind the illusionary ideas prevalent in those times. It’s high time for us to develop a sense of understanding about the greatness of ancient texts and the prowess that we had possessed. People, especially youth, should be encouraged to turn back to the forgotten pages of Indian history and restore the glory of our culture and tradition.