1. Astronomy
Earth Science

2. Johannes Kepler Kepler developed the Laws of Planetary Motion
The orbit of every planet is an ellipse.
A line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit.
Longer orbits have longer periods, and the speed of a planet in a larger orbit is lower than in a smaller orbit.
D3 = T2 D= distance in AU T= period in years
1 Astronomical Unit = 93 million miles!
Distance from the Earth to Sun

3. Practice Problem
Calculate the period of Mercury if it is 0.39 AU away from the Sun.
D=0.39 AU
T=?
D3=T = T2
T = 0.24 years

4. Practice Problem
Calculate the distance Mercury is from the Sun if its period is 0.24 years.
D=?
T=0.24 years
D3=T2 D3 = 0.242
T = 0.39 AU

5. Galileo
Discovered four moons orbiting Jupiter

6. Galileo Planets are circular disks and not just points of light
Venus has phases just like the moon

7. Galileo
The moon’s surface is not smooth

8. Galileo
The Sun has sunspots (areas of the sun with “cooler” temperatures)