Post on 31-Dec-2015
Ancient Greeks
• Observed patterns in the stars that didn’t move or change- the stars moved, but stayed in the same position relative to each other.
• Observed 5 points of light that seemed to wander among the stars – planets (wandering star)
• Mercury• Venus• Mars• Jupiter• Saturn
Earth was the center of the universe
geocentric
Greek for Earth
center
http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html
Ptolemy
• AD 140• Greek Astronomer• Earth is the center of
a system of planets• The planets move on
little circles that move on bigger circles around the earth
Curt Suplee, Milestones of Science p.24
http://www.polaris.iastate.edu/EveningStar/Unit2/unit2_sub1.htm
• This vision of the Ptolemaic universe from a 1660 celestial atlas, shows the position of the Earth surrounded by the celestial circles
• These ideas lasted for 1400 years!
Curt Suplee, Milestones of Science p.24-25
Copernicus
• Believed the sun was at the center of the universe
• Heliocentric
• His work was published in1543 – while he was on his deathbed!
Sun
Galileo
• ~100 yr after Copernicus
• Observed 4 moons revolving around Jupiter
• Observed Venus has phases like our moon
Neither of these observations can be explained with Earth at the center, therefore the sun is at the center! Copernicus was correct!!
Galileo believed the orbits are circles
Galileo cont.
Tycho Brahe (TEE koh BRAH uh)1546-1601
• Danish Astronomer – made very careful observations of the planets for almost 20 yr.