lect 2 part - ASTR 113 Section 001 Lecture 2 Development of...

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1 ASTR 113 – Section 001 Lecture 2 Development of Modern Astronomy Ancient astronomers invented geocentric models to explain planetary motions Like the Sun and Moon, the planets move on the celestial sphere with respect to the background of stars Most of the time a planet moves eastward in direct motion, in the same direction as the Sun and the Moon, but from time to time it moves westward in retrograde motion Planet is the greek word for “wanderer”
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2 Example of Mars retrograde motion • Ancient astronomers believed the Earth to be at the center of the universe • They invented a complex system of epicycles and deferents to explain the direct and retrograde motions of the planets on the celestial sphere Ptolemaic system (200 AD)
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4 Nicolaus Copernicus devised a comprehensive heliocentric model • Copernicus’s heliocentric (Sun-centered) theory simplified the general explanation of planetary motions (16 th century) In a heliocentric system, the Earth is one of the planets orbiting the Sun • Aristarchus, in 300 BC was the first to suggest a heliocentric model. • The Copernican model still required epicycles (but not to explain retrograde motion).
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lect 2 part - ASTR 113 Section 001 Lecture 2 Development of...

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