Advanced Astronomy in Ancient India

I have previously debunked the claims of Surya Siddhanta being a primary source for the beginning of Kali Yuga in 3102 BCE in my book “Yuganta-The Advent of Kali Yuga”. In this article, I hope to throw light on Indian astronomy’s mind-blowing knowledge of the universe and accuracy using the evidence of the Surya Siddhanta–possibly the oldest extant astronomy treatise in the world.

Surya Siddhanta has an elaborate discussion on the different measurements of time in days, months, years (of man, ancestors, and God), Yuga, Caturyuga, Manvantara, and Kalpa. It is stated that a divine year (1 year of Gods) is equal to 360 Human/Solar years and that 12,000 such divine years make a Caturyuga.

तद्द्वादशसहस्त्राणि चतुर्युगमुदाहृतम् ।
सूर्याब्दसंख्यया द्वित्रिसागरैरयुताहतैः ॥

(1.15) “Twelve thousand of these divine years are denominated a Caturyuga; of ten thousand times four hundred and thirty-two solar years.”

Surya Siddhanta goes on to give a calculation for the division of this Caturyuga into Krita, Treta, Dwapara and Kali Yugas.

युगस्य दशमो भागः चतुस्त्रिद्वयेक सङ्गुणः ।
क्रमात्कृतयुगादीनां षष्ठांऽशः सन्ध्ययोः स्वकः ॥

(1.17) “The tenth part of this Yuga, multiplied successively by four, three, two and one, gives the length of Krita and the other ages, in order; the sixth part of each belongs to its dawn and twilight.”

i.e., Caturyuga (X) = 12,000 * 360 = 4,320,000 years
& Y = 1/10 of X = 432,000. That makes,
· Krita Yuga is (4Y) = 1728K years
· Treta Yuga is (3Y) = 1296K
· Dwapara Yuga (2Y) = 864K years· Kali Yuga (Y) = 432K years

What is the utility of these enormous measurements of Time? As if this is not big enough, Surya Siddhanta next enumerates the number of revolutions of each planet in the duration of a Caturyuga. The planets and their revolutions are presented in the table below.

Note: Readers who are not well versed in Sanskrit can skip the below table, I have provided the Surya Siddhanta values in a summarised form later in the article.

Does it have any practical use knowing these millions & billions number of revolutions of a planet in a Yuga? As a matter of fact, it does!

It can be seen that Surya Siddhanta makes use of the number “4.32 million” because, when the Sun completes 4.32 million revolutions (i.e., years), the total revolutions of the Moon and the planets can be expressed as whole numbers/integers. In other words, 4.32 million is the lowest number in which all the planets (+ Moon’s node) will have their revolutions in integers (i.e., without any decimal).

The intricate knowledge of the movements of celestial objects and the sheer ability to even comprehend & come up with this huge common denominator is a herculean achievement in itself. But Surya Siddhanta takes this feat one step further!

The total number of revolutions obtained in the previous step can be used to accurately calculate the orbital periods of these celestial bodies. Verse 1.34 quoted above gives the logic of Surya Siddhanta to calculate the number of risings of the planets— “The number of risings of the asterisms, diminished by the number of revolutions of each planet respectively, gives the number of risings of the planets in a Yuga.”

The number of risings of Asterisms = 1,582,237,828
The number of revolutions of the Sun in a Yuga = 4,320,000

Now, understand that the “rising of the Sun” is nothing but “the commencement of a civil day” and thus “number of risings of the Sun” will correspond to the “number of civil days”.

Therefore, Number of civil days = Asterisms (no. of risings) – Sun (no. of revolutions) = 1,577,917,828

Once we know the number of civil days and the number of revolutions of a planet, we can easily calculate the Orbital period of the planet.

For example: If we are given the information that the Earth completed two revolutions in 730 days, we can infer that Earth takes 365 days to complete one revolution.

Therefore, Orbital period = Number of Civil days/ Number of revolutions

So, the Orbital Period of the Sun becomes: 1,577,917,828/ 4,320,000 = 365.259 days

Note: The orbital period of the Sun found from the above calculation should be understood as the orbital period of the Earth. Because the number of revolutions of the Sun as observed by an astronomer stationed on Earth is in effect the number of revolutions of planet Earth around the Sun.

Similarly, The orbital period of the Moon = 1,577,917,828/ 57,753,336 = 27.322 days
The orbital period of the Mercury = 1,577,917,828/ 17,937,060 = 87.970 days
The orbital period of the Venus = 1,577,917,828/ 7,022,376 = 224.699 days
The orbital period of Mars = 1,577,917,828/ 2,296,832 = 686.998 days
And so on…

The remarkable accuracy achieved by the astronomers of the Surya Siddhanta can be appreciated when their calculations are compared alongside the orbital values obtained using modern scientific tools.

It should also be noted that while the solar system is largely stable, the planets and their orbital periods do vary with time over both short and long duration and thus the numbers obtained can change depending on how long the measurements were conducted. Considering this, it is important to remember that Surya Siddhanta’s orbital periods are not necessarily erroneous (even if very small). In fact, they could well be the most accurate measurements of the time when they were calculated.

However, more than the accuracy of these values derived from Surya Siddhanta’s calculations, the mere fact that our ancient Indian astronomers had the knowledge and the ability to even conceive these elaborate calculations to obtain the orbital periods is what impresses me the most.

You may ask, what is the use of knowing the orbital periods of far away Planets? What difference does it make for a common man?
Well, what day is it today? what day comes after a Sunday?
Have you ever thought, why is a Friday always preceded by a Thursday?

If you haven’t already guessed it; the orbital periods of the Planets are the foundation for the “sequence of weekdays” that is being followed worldwide! But that’s a story for another time.

To Summarize,
· Surya Siddhanta states that one Caturyuga lasts for 4.32 million years.
· Surya Siddhanta makes use of 4.32 million years because 4.32 million is the lowest number in which the revolutions of all the planets (+ Moon’s node) can be represented in integers.
· Surya Siddhanta also provides the number of revolutions each planet has in a Caturyuga, using which one can calculate the accurate orbital period of the planets.
· Orbital period of the planets is the foundation for the “Sequence of the weekdays” that is being observed worldwide.

Yuganta-The Advent of Kali Yuga:
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