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 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

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 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