The first Greek to observe ocean tides, in the Atlantic in the early third century B.C., was the navigator and astronomer Pytheas, who also produced the correct explanation for them. He was 2,000 years ahead of his time; Sir Isaac Newton was the first person to correctly attribute them to the influence of the moon. Before Newton's time, most scholars refused to believe that the moon could have any effect on the ocean, especially because one tide each day took place when the moon was not even visible in the sky.