Human efforts to make sense of the universe undoubtedly began long before the dawn of civilization, but the speculations of the first stargazers can never be known. We do know that more than 2,000 years ago among the ancient Greeks, at least one person—the philosopher Aristarchus—believed that the Earth and other planets revolved around the sun.
Aristarchus and another Greek who came before him, Democritus, also pondered the stars, theorizing that they were other suns. Democritus was one of the boldest thinkers in ancient Greece. He proposed that everything is composed of atoms and that the hazy band of light across the sky formed by our own Milky Way galaxy was made up of stars too far away to be seen as individual pinpoints of light.
The ideas of Aristarchus and Democritus were revolutionary for their day. If their views had prevailed, the modern age of cosmology might have begun much sooner.