Some selected discoveries. Rigvedic calendar 360 days, 12×30, but average is 365 days over 6 years because of correction month. Jyotishya Vedanga records astronomical data 4000 BCE. Sage Yajnavalkya 3000 BCE, propounded the heliocentric model. Satapata Brahmana, he measured the distance from earth to sun, earth to moon at 108 times diameter of the Sun and Earth. Modern figures are these. Surya Siddhanta has got lot of complex astronomical and time measurements. 2000 years ago Indians proposed stars were like the sun, but further away. Aryabhatta had something that looked like a partial heliocentric model. He knew that the shadows of the earth, shadows of the moon because of the sun shining on it. He also had formulas to compute the length of the shadows and if an eclipse will happen and all those kinds of things. Varahamihira said the same force that holds object to the earth also holds celestial bodies in its place. Brahmagupta calculated earth’s circumference at 36,000 km. Bhaskara II calculated Precession of Equinox at 25461 years. The same Precession that I have been talking about. Bhaskara II put it down to 25441 years. Very, very accurate figure that has not bettered upon until European science around 19 century. Sayana who is the minister, the prime minister in Vijayanagara, he in his commentary on the Rig Veda computed the speed of light. Subash Kak shows that his 2202 yoganas and ½ nimisha translates to this figure, very modern figure.
Surya Siddhanta. Amazing book, you can download this from Google and read it. It contains chapters on astronomy, time cycles and planetary diameters. Yup, you heard me right. It talks about planetary diameters. Not only were the ancient Indians observing these planets as blobs of light moving in the sky, but they also knew those blobs of light have got a diameter, a physical dimension associated with it. And they were able to compute it. So Surya Siddhanta lists Mercury at not in miles obviously, these are modern interpretations 3008 miles. The true figure is so much. Saturn at 73,882 miles this is a true figure. Mars at 3772 miles this is a true figure Venus and Jupiter, they made some mistakes in getting those things.
Now you may wonder how on earth did they do that? Whether it is 700 BCE or 480 current era. How on earth did they do that? They didn’t have telescopes. How did they do that? Well it turns out that they used Trigonometric ideas. One idea if you have the half moon directly overhead of you, you know that the illuminated face of the moon comes 180° away from the sun. You know that if this distance from you to the moon is 1 then the angel is 1/7 of a degree. Then this is 400 a right angled triangle property. Using these ideas and using ideas that everybody has done integration in high school knows about. If you did Reman integration, you know that you had to draw a lot of lines over there in your graph paper and summing the area under the curve, the lines help you to get a better and better figure. Similarly the ancient Indians in order to compute tithi, they needed to compute tithi, when a particular tithi would pass and so on and as accurately as possible. So they would divide the nakshatra from one to other by finer lines of resolution which will allow them to map the movement of heavenly bodies in a much finer way. So by making use of how quickly the bodies are moving and by using Trigonometric ideas they were able to estimate this planetary diameters. That is the ingenuity of our ancestors that we need to connect to. This is lost in the popular discourse completely. We have no idea. We don’t even talk about these things.
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