Ptolemy

Aristarchus (ahr-uh-STAHR-kuhs; c. 270 b. c.) had advanced the heliocentric (heel-ee-oh-SEN-trik) view of astronomy, holding that the Earth and other planets revolve around the Sun. Hipparchus (see entry), however, adopted a geocentric (jee-oh-SIN-trik) view, claiming that the Earth is fixed, and the Sun and other planets revolve around it. Unfortunately, the Alexandrian astronomer Ptolemy (TAHL-uh-mee), an influential follower of Hipparchus, accepted the geocentric view.

Ptolemy—not to be confused with the Greek ruler of Egypt and his descendants—developed a system of astronomy that would remain in use for some fourteen centuries. When science flourished in the Arab world during the Middle Ages, his book—known by its Arabic name, Almagest—became the bible of astronomy. Because of this, the geocentric view became the standard opinion until Nicholas Copernicus (kuh-PURN-i-kus; 1473-1543) disproved it.

Greek astronomer Ptolemy mistakenly believed that the Sun and other planets revolved around the Earth.

Library of Congress.

Ptolemy also shared in Hipparchus's rejection of calculations made by Eratosthenes (ur-uh-TAHS-thuh-neez; c. 276-c. 194 b. c.) The latter, a librarian of Alexandria, had made a remarkably accurate measurement of the Earth's size. Because of Ptolemy's mistaken understanding, Christopher Columbus (14511506) would later drastically underestimate the westward distance from Europe to Asia; as it turned out, there was a whole New World in between.