History of Astronomy — Ancient Egypt

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History of Astronomy — Ancient Greece


Ancient Greece. Aristotle The ancient Greeks produced theories based upon many practical calculations of the Egyptians. Thales, a Greek merchant who lived from about 640 to 550 B.C.E., traveled extensively in Egypt. He spent time talking with priests there, and learned their secrets of mathematics and astronomy. When he retired from his travels, he took up philosophy and mathematics, bringing what he learned from the Egyptians to Greece. He also sent his young student, Pythagoras (ca. 584-495 B.C.E.), to Egypt to learn from these priests. Pythagoras exceeded his master's abilities and formed a secretive school. As his students grew older and traveled, some wrote down their formerly secret teachings. Shown at left is a statue of the most famous ancient Greek philospher of all, Aristotle.

Eventually Plato obtained documents of Pythagoras' student Philolaus, and he personally knew another Pythagorean student, Archtas. In this way, Plato was able to write of some of the discoveries of that previously secret school. In Plato's day, the Earth was widely believed to be a sphere from observations of the constellations made at different latitudes.

Hippocrates discovered some basic mathematical formulas such as the area of a circle. His originial works are lost, but his mathematical discoveries are preserved in Book III of Euclid's Elements. Archimedes followed Euclid, and devised numerous trigonometric and other formulas.

The Greek astronomer Meton (5th century B.C.E.) found that 19 solar years corresponded almost exactly to 235 lunar months. A "lunar year" is 12 lunar months. 19 lunar years is 12 x 19 = 228 lunar months. Meton added 7 more months in his cycle to synchronize the lunar and solar calendars. This was later adopted as the standard for the Jewish calendar.

Aristotle's contribution to philosophy, science, and many other areas was unparalleled by any other Greek writer. However, he did make some statements that were not true and yet were held as beliefs until the time of Galileo. One of his statements was that heavier objects fall faster than lighter objects. He also believed that the Sun and all the planets revolved around the Earth. Aristotle also believed that a projectile (a thrown object) traveled first at an upward angle, then down in a straight line. This might appear to be the case if you are throwing an object and observing it from your location, but an observer looking at the thrown object from the side can see that this is not so. Mose scholars of the Middle Ages treated the words of Aristotle as beyond questioning. It took experiments by Galileo and others of his time to break from these Aristotlean beliefs.

Alexander the Great collected many of these early works in his famous library in Alexandria, where construction began two years before his death in 321 B.C.E. The library came under Claudius Ptolemy (ca. 100-168 C.E.), who in his famous Tetrabiblos and Almagest summarized much of the thought in mathematics, astronomy and astrology from Greece's Golden Age. His Ptolomaic system of planetary theory stated that the Sun revolved around the Earth. The Ptolomaic system was the standard in Europe for about 1400 years, when Copernicus demonstrated that the Earth revolved around the Sun.

Before Ptolemy, Aristotle's friend Aristarchus stated that the Earth revolved around the Sun. However, Aristotle adopted the theory of Eudoxus of the Earth being the center of the Universe.

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