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The move to a heliocentric world view. 1. Scorpius. (Sept ‘99). MARS. Antares. southwest. Scorpius. (Sept ‘99). 4. 1. Antares. Scorpius. (Sept ‘99). 7. 4. 1. Antares. Scorpius. (Sept ‘99). 10. 7. 4. 1. Antares. Scorpius. (Sept ‘99). 13. 10. 7. 4. 1. Antares.
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1 Scorpius (Sept ‘99) MARS Antares southwest
Scorpius (Sept ‘99) 4 1 Antares
Scorpius (Sept ‘99) 7 4 1 Antares
Scorpius (Sept ‘99) 10 7 4 1 Antares
Scorpius (Sept ‘99) 13 10 7 4 1 Antares
Scorpius (Sept ‘99) 16 13 10 7 4 1 Antares
Scorpius (Sept ‘99) 19 16 13 10 7 4 1 Antares
Scorpius Wanderers “planets” MercuryVenusMarsJupiterSaturn (Sept ‘99) 22 19 16 13 10 7 4 1 Antares
The astronomer must try his utmost to explain celestial motions by the simplest possible hypothesis; but if he fails to do so do, he must choose whatever other hypotheses meet the case. -Ptolemy of Alexandria (140 A.D.)
Ptolemy’s Epicycles Epicycle Deferent
Ptolemy’s Epicycles Where is retrograde motion?
Maintaining the use of perfect circles and constant orbital rates, he invoked the use of epicycles moving on deferents.
not quite right: modified the model with the Earth slightly off center
Had to arbitrarily “peg” Mercury and Venus between Earth and Sun.
Ptolemy to the Renaissance • Ptolemy’s work kept alive by Arab astronomers • DOMINATED FOR NEARLY 1500 YEARS!
Nicolaus Copernicus (1473-1543) “A system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind.”
De revolutionibus -1543 On the Revolutions of the Heavenly Spheres
The Copernican Model • heliocentric (sun-centered) • stars are very far away • Earth rotates on axis • Earth revolves around Sun
Pisces Aries Earth Gemini The Sun’s Apparent Motion Around the Ecliptic.
Pisces Aries Earth Gemini The Sun’s Apparent Motion Around the Ecliptic.
Pisces Aries Earth Gemini The Sun’s Apparent Motion Around the Ecliptic.
Epicycles? Problem: Copernicus still could not predict the planet’s positions accurately with circular orbits. Solution: Re-introduce epicycles! Question: Is this any simpler?