Early Observations
Greek Observations
• Saw star patterns in the sky travel together
(Constellations)
Early Observations
• Some stars seemed to wander (planets)
• They were later named by the Romans(Mercury, Venus, Mars, Jupiter, Saturn)
Early Observations
• Most Greek astronomers believed that Earth was in the center of a celestial sphere. (geocentric system)
Early Observations
Claudius Ptolemy
• Earth in center• Planets move on small circle that move on bigger circles• Widely accepted for 1500 years
Early ObservationsNicholas Copernicus• Believed in a sun centered
system (Heliocentric)
• Said the planets moved around the sun in circles in 1543
Mikolaj Kopernik
Early ObservationsNicholas Copernicus• He was banned by the
Catholic church
• Galileo used the telescope to support him (Venus phases, Jupiter’s moons)
• He was placed under house arrest
Mikolaj Kopernik
Galileo
Early Observations
Johannes Kepler
• Analyzed Brahe’s observations and found that the path of the orbits were ellipses
• Kepler’s 1st Law
Early Observations
Johannes Kepler
• He found that the speed of orbiting planets is constantly changing
• Kepler’s 2nd Law
Early ObservationsJohannes Kepler• When he compared
planets, he found a relationship between how far from the sun they were and the time to make one orbit
• Kepler’s 3rd Law
Early Observations
Today we know of 8 planets (MVEMJSUN) their moons, and smaller objects that revolve around the sun
What about Pluto?
• According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.
• Pluto does not dominate its neighborhood
Charon is half it size
It does not sweep up its neighborhood, there is
much debris in its orbit