Select the best introductory sentence for the following paragraph.

As long ago as 300 B.C., a Greek astronomer named Aristarchus came to the conclusion that the sun stood still while the earth and other planets revolved around it. Using only his naked eye because there were no telescopes in those days, Aristarchus determined that the passing of night and day and the changing of the seasons could all be explained by viewing the heavens in that way.