Great Astronomers of Ancient Greece
As follows are 10 great scientists of ancient Greece, who made pioneering discoveries in the field of astronomy:
Thales (Miletus, 624-548 B.C.E.)
Thales was notable for his teaching that the Earth sprang from a primordial mass of water. Nevertheless, he was able to accurately measure the apparent diameter of the sun through the use of geometry, as well as explain the nature of a solar eclipse. Thales also defined the constellation Ursa Minor and its usefulness for purposes of navigation.
Anaximander (Miletus, ca. 610–ca. 546 B.C.E.)
A pupil of Thales, Anaximander taught that Earth moves freely in space at the center of the Universe. He correctly asserted that the Earth’s surface was curved, but mistakenly assumed it to be cylindrically-shaped. Thales also noted that the heavens seem to move around Polaris (the North Star), and used a complete sphere to locate stars and planets in the night sky.
Pythagoras (Samos, 572–492 B.C.E.)
Pythagoras taught that the Earth was a perfect sphere at the center of the Universe and that all celestial objects, also spherical in shape, moved in circles around it. He correctly reasoned that the Moon’s orbit was inclined to the Earth's equator, and was the first to explain that both the morning and evening stars were the same celestial body: the planet Venus.
Anaxagoras (Clazomenae, ca. 500 B.C.E.)
Anaxagoras wrongly believed that all matter was composed of air, and that the Sun was a huge, hot stone. However, he correctly proposed the Moon shone by reflected sunlight or false light; and explained that shadows on the Earth caused by the Sun and Moon are responsible for the solar and lunar eclipses/phases.
Eudoxus (Cnidus, ca. 400–347 B.C.E.)
Through the application of mathematics, particularly geometry, Eudoxus contributed to the concept of apparent movement of fixed stars and constellations over a one-year period. He was the first to propose the geocentric view of the universe, in which Sun, Moon, planets, and stars moved around a motionless Earth on a series of 27 crystal-like celestial spheres.
Heraclides (Pontus, ca. 388 B.C.E.)
Heraclides was the first to suggest that the seeming westward motion of heavenly bodies across the sky was the result of eastward rotation of the Earth on its axis. Though he incorrectly advocated the geocentric theory, he boldly speculated that the planets Mercury and Venus revolve around the Sun.
Aristotle (Macedonia, 384–322 B.C.E.)
Though Aristotle was regarded to be one of the most influential thinkers in history, he erroneously endorsed a geocentric cosmology, in which a motionless spherical Earth is surrounded by a system of 56 concentric crystal spheres, each serving to account for all movements of visible heavenly bodies. His view of the universe dominated Western thinking for nearly two millennia until eventually succumbing to the heliocentric or Sun-centered theory of Nicholas Copernicus, Johannes Kepler and Galileo Galilei.
Aristarchus (Samos, ca. 320–ca. 250 B.C.E.)
Aristarchus is credited as the first to propose the heliocentric model of the cosmos, seventeen centuries before Copernicus resurrected the theory. He suggested that the Earth not only rotated on its axis but also orbited the Sun along with other known planets. Aristarchus was also the first astronomer to apply mathematics, albeit inaccurately, in determining the distance between the Earth and the Sun.
Hipparchus (Rhodes, ca. 170–125 B.C.E.)
Although Hipparchus was a staunch geocentrist, he is widely regarded by historians as the greatest astronomer of ancient times. Through geometric calculations and his own observations, he realized that the Earth moved--not the stars. Hipparchus was the first to compile of the first star catalogue of about 850 stars; divide of naked eye observations into six magnitudes from the faintest to the brightest observable object in the night sky; and calculate the first realistic measurements of the Earth’s distance from the Sun and the Moon. He also carefully studied the Sun’s movement to estimate the length of the year within 6.5 minutes from now-accepted figure.
Ptolemy (Alexandria, ca. 90–170 C.E.)
Certainly the most influential of the ancient astronomers, Ptolemy wrote the 13-volume called the Almagest, which contained the astronomical and mathematical knowledge of all the ancient Greek philosophers and astronomers. Ptolemy built on the work of many ancient astronomers: he expanded Hipparchus’ catalog of 850 stars to include 1,022 stars, and extended Aristotle’s teachings to develop his Ptolemaic system of planetary motion. Despite some inaccuracy of his astronomical charts and his belief in the geocentric model, his work stood unopposed until the scientific revolution of the 16th century.
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