The 18th shloka in Hanuman Chalisa talks about Hanuman jumping to sun thinking it is a fruit. It is now suggested that the particular shloka in Hanuman Chalisa calculates the distance between earth and sun. Hanuman Chalisa was written during the 15th Century.
The 18th Shloka reads like this: Yuga Sahastra Yojan Par Bhanu Liliyo Tahi Madhur Phal Janu
Yuga means the sum of Four Yugas (1 complete Mahayuga) with unit in divine years. Sahastra is 1000. Yojan is 8 miles. Bhanu is Sun
Satyayuga= 4800 divine years Tretayuga=3600 divine years Dwaparyuga=2400 divine years Kaliyuga=1200 divine years
So 1 Mahayuga= 12000
Now next is sahastra common Sanskrit word meaning “1000″
Next is “Yojan” also know as that equals to 8 miles
Yuga X Sahastra X Yojan (in miles) = 12000X1000X8= 96,000,000 miles Now 1 mile= 1.6km
So 96,000,000 miles= 96,000,000X1.6 km = 153,600,000km.
Today estimated distance is approximately 150,000,000 km which is close to above.
Note – There are some doubts in the above theory; By Yuga did Tulsidas mean a Mahayuga. In some translations the Yuga Sahastra Yojan is given as Juga Sahastra Yojan. Juga then mean 12000 years in that interpretation.
This is not a final statement. You should look for the correct interpretation of the Shloka in books and if possible talk to scholars about the translation of the 18th Shloka. Then come to a conclusion.