1. Observing the Solar System
Section 20.1

2. Early Observations Greek Observations
Saw star patterns in the sky travel together
(Constellations)

4. Early Observations Some stars seemed to wander (planets)
They were later named by the Romans
(Mercury, Venus, Mars, Jupiter, Saturn)

5. Early Observations
Most Greek astronomers believed that Earth was in the center of a celestial sphere. (geocentric system)

6. Early Observations Claudius Ptolemy Earth in center
Planets move on small
circle that move on
bigger circles
Widely accepted for
1500 years

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

8. 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

9. Early Observations Tycho Brahe
Made accurate observation for over 20 years

10. Early Observations Johannes Kepler
Analyzed Brahe’s observations and found that the path of the orbits were ellipses
Kepler’s 1st Law

11. Early Observations Johannes Kepler
He found that the speed of orbiting planets is constantly changing
Kepler’s 2nd Law

12. 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

13. Early Observations
Today we know of 8 planets (MVEMJSUN) their moons, and smaller objects that revolve around the sun

14. 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