Earth's radiation budget provides an inventory of the energy received and lost by the Earth's climate system, soil-atmosphere-oceans. The energy input comes mainly from the Sun, the one produced in the center of the Earth representing only 0.01% of the total energy received by the surface of the Earth.
Yes, it is believed that one of the first Greek ancient astronomers, and the first notable Greek philosopher, was Thales, who lived at the beginning of the 6th Century BCE.