Ramayana narrates the episode when Lord Hanuman as a child thought the sun to be a fruit and went up to it and put it in his mouth. Hanuman Chalisa, written by Bhakti Kaal poet Tulsi Dasji describes this incident in the following verse,
Yug sahasra yojan par bhanu
Leelyo tahi madhur phal janu
The verse translates as ‘sun, which rests at a distance of yuga sahasra yojanas, by thy leela appeared as a sweet fruit.
What is incredible here is the accuracy in reporting the distance of sun from the earth,
1 yuga = 12000 years
1 sahasra = 1000 units
1 yojan = 8 miles
So the given distance of sun is, 12000*1000*8 miles, which is 96000000 miles.
1 mile = 1.6 km
So in kilometres the distance comes to be 1536000000 kms
This figure is very close to the distance of sun from earth as calculated by modern equipment during the period when earth is farthest from the sun (aphelion), which stands at 152,093,481 kms!
While Hanuman Chalisa was given by Tulsi Dasji in the 16th century, and it appears he only included a detail which was known to the vedic seers since long, it was only in 1653 that astronomer Christiaan Huygens for the first time estimated the distance of sun from earth through his guesswork. And it was in 1673, that Giovanni Cassini was given the credit for calculating the distance of sun from earth, since Huygens findings were based on guesswork.