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A Brief History of A Brief History of AstronomyAstronomy
350 bce. - mid 1600’s ce.350 bce. - mid 1600’s ce.
Aristotle's Theory : 350 bceAristotle's Theory : 350 bce
• Geocentric model of the Earth– Earth is the center of
the universe– Earth does not move – Everything circles the
earth
The ProblemThe Problem
• Retrograde Motion– Or Wandering Planets
Mars and Venus appear from earth to move backwards in their orbit
Ptolemy’s Solution 140cePtolemy’s Solution 140ce490 years later490 years later
• Based on 80 perfect circles
• Large circles -Deferents
• Small circles -Epicycles
• BUT:• Very complex -
Could call it messy
13 centuries later:13 centuries later:1543 ce1543 ce
• Copernicus: Heliocentric model• Earth is not the center of everything• Earth only center of moon’s orbit• All planets revolve around the sun• Universe is unbelievably large• Any motion seen in the stars is result of earth’s
motion• Sun does not move – its motion is a result of earths
movement• Retrograde motion can be explained by earth’s
motion
No One Listened!No One Listened!Why?Why?
• Published after Copernicus’ Death
• No Mathematical model to back it up
• Published in Latin: Which was not widely read
• It went against:– Tradition– The Catholic Church (cultural
power)– Common sense
1608 ce:1608 ce: Birth of Modern Astronomy Birth of Modern Astronomy
• Galileo– Use Telescope to look into space– Discovered:
• mountains, valleys, and craters on the Moon
• That the Sun rotates once a month (Sun Spots)
• Four moons of Jupiter • Phases of Venus
– Brought focus back to Heliocentric model
Galileo’s TrialsGalileo’s Trials• Heliocentric model still went against:
– Tradition– The Catholic Church (cultural Power)– Common sense
• Forced to retract theory by Catholic Church*
• Goes blind from looking at the sun• Dies under house arrest • Feud with Tycho Brahe
– Collecting data to support Geocentric model during the same time
– Working for the Catholic Church
Sweet Irony Sweet Irony (just a few years after Galileo)(just a few years after Galileo)
• Brahe’s assistant: Kepler – Feared by Brahe– Assigned to Mars– Uses Mars's Retrograde motion to build a
mathematic model supporting Galileo– Published in 1621 ce
• More on Kepler later• Newton’s laws of motion
– mid 1600’s– explained the motion outlined by his
predecessors
To Sum Up To Sum Up
Aristotle350 bce
Ptolemy140ce
1543 ce Copernicus
Galileo1608 ce
Kepler1621 ce
Newton’s laws of motion1685 ce
BraheAdopted
by the C.C.1616ce
Geocentric
Heliocentric