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Greek Astronomy. Ancient View of the Cosmos. Universe is 2-D All celestial objects attached to a sphere. Celestial Sphere is close Climb a high mountain and touch the sky Celestial objects are self-luminous Earth is the center of the universe Objects move on perfect circles.
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Ancient View of the Cosmos • Universe is 2-D • All celestial objects attached to a sphere. • Celestial Sphere is close • Climb a high mountain and touch the sky • Celestial objects are self-luminous • Earth is the center of the universe • Objects move on perfectcircles
Pre-disposition for success • Not Fatalists like Babylonians • Greeks had a curiosity about nature • Model builders
Lunar Phases and Eclipses Two important changes in thought needed • Universe is three dimensional • Some celestial objects are dark
Lunar Phases Phases
1st Quarter Full Moon New Moon
Moon (3476 km) Earth (12,756 km)
Lunar Eclipses Sun penumbra umbra Moon Earth
Lunar Eclipses • Eclipse shadow is always a section of a circle • Earth must be a sphere • Color of the eclipsed moon
North Pole Equator Alexandria 7° Sun’s Rays Syene Eratosthenes Video
Eratosthenes • 7° is about 1/50th of a circle • Alexandria and Syene are separated by 800 km • That 800 km must be 1/50th the circumference of the Earth • Earth Circumference = 800*50 = 40,000 km • Accepted value is 40,074 km
Relative sizes and distances • By 350 BC Greek Natural Philosophers knew the relative diameters and distances of the Sun, Moon, and Earth. • The Sun was very large and very far away and the Earth was bigger than the Moon.
Cosmologies • Heliocentric Model • Aristarchus of Samos
Cosmologies • Geocentric Model • Aristotle 350 BC
Stationary Earth • Earth is heavy • Easier to imagine the sky can move • It looks like the sky is moving • We have no sensation of our motion • Rotating Earth would make objects fly off of the surface • StellarParallax
June January Stellar Parallax • Hipparchus 150 BC Sun
Why did Hipparchus fail to observe Stellar Parallax? • He only looked at bright stars. • He was a poor observer. • The stars are too far away. • The Earth does not orbit the Sun. 10
Aristotelian UniverseTerrestrial Realm Earth and Water tend to sink • Composition predicts motion • natural tendencies Fire and Air tend to rise • Overall tendency to seek rest • Objects following tendencies require no force • Objects are corruptible (changing)
Aristotelian UniverseCelestial Realm • Celestial Objects composed of Aether Self luminous but does not consume • Motion is constant,circular • Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere
Claudius Ptolemy (150 AD) • Accounted for retrograde motion within the confines of the Geocentric Model
Earth Moon The Sun and Moon
Deferent Epicycle Planet Earth The Planets Link
John Milton, Paradise Lost • With Centric and Eccentric scribl'd o're, Cycle and Epicycle, Orb in Orb
Astronomy in the Dark Ages • Fall of Rome • Greek knowledge went to Islam • Alexandrian library destroyed • Universal Illiteracy • No mass communications • Villages were isolated • Thomas Aquinas • Giordano Bruno