Kepler’s LawsYep, all three!

Greek ObservationsEarly Greeks were the first to truly notice

the planets in our solar system. In fact, planets is Greek for wanderers.

Greeks believed that the earth was spinning within a larger dome called the celestial sphere.

Greeks believed in a geocentric model, where the earth is at the center.

Ptolemy (Greek astronomer)

Ptolemy believed, as other Greeks did, that Earth was at the center; however, he hypothesized that the planets were moving on flat planes.

The Geocentric model was accepted as truth for nearly 1,500 years!

Copernicus’s Revolution!

Polish Astronomy, Nicolaus Copernicus helped to develop the heliocentric model, where the sun is at the center rather than the Earth.

Many people had trouble accepting this model, even into the 1600’s!

Good old Galileo GalileiBecause Galileo use the newly invented

telescope, he was able to discover more than his predecessors.

Galileo discovered 4 moons orbiting Jupiter (known as the Galilean Moons)

Galileo also helped to support and develop the heliocentric model.

Tycho Brahe & Johannes Kepler

Late 1500’s, Danish astronomer Tycho Brahe and his assistant Johannes Kepler worked over a 20 year period collecting data through observations of the night’s sky.

After Brahe died in 1601, Kepler continued to analyze and study the data- from that came his 3 laws.

Kepler’s 1st Law

Through his observations of Mars’s orbit, he discovered his first law:

The Orbital path of the planets are NOT circular- they are an ellipse (oval shape).

This discovery disproved the long help belief of circular orbits.

Kepler’s 2nd Law

Kepler then discovered that the speed of a given planet changes as it revolves around the sun.

The closer a planet is to the sun, the faster it moves. The farther away it is, the slower it moves.

Kepler’s 3rd Law

Kepler also discovered that the time it takes a planet to orbit the sun and it’s average distance from the sun are directly related.

The closer a planet is to the sun, the faster it’s revolution. The farther a planet is, the slower the revolution.