MULT10011 Lecture Notes - Lecture 23: Aberration Of Light, Deferent And Epicycle, Heliocentrism
15 Jun 2018
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L.E.U - Lecture 23
Cosmology
• Watching the night sky
o While starts rotate across the sky, the relative position of any two starts is
fied
o 7 moving celestial bodies – they blod out stars as they move (in front of stars)
▪ Sun, Moon, Mercury, Venus, Mars, Jupiter & Saturn
Dawn of scientific astronomy
Greeks – Plato, Aristotle
• Simple models that can be tested against observations
• Predict planet/star motions by placing them on rotating spheres around Earth
o Finite universe – solar system
o Explained gravity – earth stuff moves to centre, fiery stuff rises
o Eplais h e dot feel otio
o Eplais h stars dot oe/pass i frot of eah other sae sphere
▪ Circle/sphere is a mathematically special shape
• Prole: otios dot alas look like irles
o Ptolemy addressed this by adding epicycles (~50 spheres, not 8)
▪ Ptolemaic model frames understanding until telescope
Heliocentrism?
• First mathematical version (with same epicycles as Ptolemy) – Copernicus
• Apparent flaws:
o In an infinite universe, why is the night sky dark? – Olber’s paradox
o If the earth is oritig the su, h dot the positios of starts shift durig
the year? – parallax
Telescopes – not everything rotates around Earth
• 1610s: Galileo discovered moons around Jupiter, phases of Venus, and the apparent
rotation of the sun (evidenced by sunspots)
• 1639: with a telescope, Zupi saw phases of Mercury
theory: the end of epicycles for Heliocentrism
• 1609: Kepler introduced elliptical orbits – allowed model to match observations
• 1687: Isaac Newton – universal gravity explains elliptical orbits
telescopes – Earth is moving
• 1725: Bradley discovers stellar aberration while looking for parallax
• 1838: 3 astronomers measured parallaxes
sizes
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