Observing the Solar System Section 20.1

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 Observations Nicholas Copernicus Believed in a sun centered system (Heliocentric) Said the planets moved around the sun in circles in 1543 Mikolaj Kopernik

Early Observations Nicholas Copernicus Was banned by the Catholic church Galileo Used the telescope to support him (Venus phases, Jupiter’s moons) Was placed under house arrest Mikolaj Kopernik Galileo

Early Observations Tycho Brahe Made accurate observation for over 20 years

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 Observations Johannes 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