Big Bang Theory

The First Cosmologies

The Greek philosophers moved the study of the universe away from a strictly religious approach to a more naturalistic one. Aristotle's ideas influenced philosophers and scientists in the West for centuries. His observations of celestial events convinced him that the earth was spherical rather than flat like a pancake. During lunar eclipses, Aristotle noted that the shadow of the earth on the moon was always round, an impossibility if the earth were flat. A flat planet would have cast an elongated shadow, not a round one (unless he always made his observations when the sun was directly under the earth, an unlikely event). Aristotle made another observation that convinced him of the roundness of earth. He saw the sails of ships coming over the horizon before the rest of the vessel. (On a perfectly flat earth, Aristotle's first view would have been of the entire ship, not just its mast.)Although some of Aristotle's conclusions about the universe were accurate, others were not. For example, he remained steadfast in his conviction that the earth was stationary and the moon, sun, other planets, and stars moved in perfectly circular orbits around the earth.

The impact of both religion and philosophy on cosmology diminished with the growth of the physical sciences. Nicholas Copernicus, a Catholic priest, suggested in 1514 that the sun was stationary and the earth and other planets moved in circular orbits around it. Copernicus's heliocentric view was discounted for nearly a century until two astronomers, the Italian Galileo Galilei and the German Johannes Kepler, reaffirmed Copernicus's deductions. The invention of the telescope (in Holland) in the early [Page 346]1600s allowed Galileo to observe stars, planets and their movements, meteors, and comets. It was during his observation of the movement of Venus that he realized Copernicus was right to believe that the earth moved around the sun. Kepler, like Copernicus and Galileo, concluded correctly that planets rotated elliptically around the sun, although he erred by thinking it was magnetic forces that were responsible.

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