Was the Speed of Light known in 13th century India? The following links claim that there is evidence of the correct speed of light in a Rig Veda Commentary: Quora: Did Sayana know the Speed of Light Speed of light in the Rig veda > In the hymn, the author pays respect to the one who moves 2202 yojanas in half a nimish The metric conversions to support this are: > 1 yojan = 4 kose > > 1 kose = 8000 British yards > > 1 British yard = 0.9144 m. and > In the Shrimad Bhagavad: > > 15 nimishas = 1 kashta > > 15 kashtas = 1 laghu > > 30 laghus = 1 muhurta > > 30 muhurtas = 1 diva-ratri If these conversions and the hymn are true, then the claim follows (Speed of light under these conversions and using the hymn calculated as 302031036.422 m/s, which is very accurate) * Is the hymn by Sayana in the 13th-something century * Are the conversions correct?

This looks very much as if the units may have been converted to obtain the desired result. Indeed the different conversion factors but similar result in your second link increase the likelihood that there may cognitive bias involved

For example, your distance conversions lead to 1 yojan being 29.2608 kilometres. Compare this with Wikipedia's 12–15 km and your second link's 9.09 miles (about 14.5 km)

Similarly on time, your calculation gives 202,500 nimishas (twinklings of the eye) in a day-night while Wikipedia quotes Manusmṛti to give 486,000 and your second link gives 409,050

Both references reach the same result by different conversion factors, which implies they're both biased and unreliable.