Greeks Discovered the planets Planet is the greek word meaning wanderers Called wanerers because they sometimes moved in the opposite direction from the rest of the visible stars in the sky

Geocentric - Earth is at the center of the solar system all planets, stars and our sun revolves around the Earth

Ptolemy’s model Greek astronomer Planets move on small circles along their orbit animation

Heliocentric Sun at the center of the solar system Copernicus Worked out the arangement of the known planets and how they moved around the sun (just a way to know where a planet is located at any given time) Animation

Galileo Used telescope to see moons revolving around Jupiter Why was this important? Also noticed that full phase of Venus is much smaller than cresent phase of Venus Why was this important? Contradicts previous view that everything in the solar system revolves around the Earth.

Venus is further from the Earth at full phase. Therefore, it is smaller in size. When Venus is in cresent phase it is close to Earth. Larger.

Venus Phases from Earth

comparison between geocentric and heliocentric models comparison between geocentric and heliocentric models

Tycho Brahe Over 20 years of detailed observations recording the location of the planets

Kepler Found that the orbit of each planet is an elipse Ellipse - Oval shaped, 2-foci

Ellipse vs. Circular Orbit