1. EARTH SCIENCE MRS. DAVIS
The Universe
EARTH SCIENCE
MRS. DAVIS

2. Our View of the Cosmos
Astronomy has seen 3 scientific revolutions in cosmology…
2nd Century: Claudius Ptolemy (Physics of Aristotle)
Geocentric: Earth-centered model of the universe
16th Century: Nicolaus Copernicus (Physics of Newton)
Heliocentric: Sun-centered model of the universe
20th Century: Edwin Hubble (Physics of Einstein)
Big Bang Cosmology

3. Geocentric Model

4. What’s wrong with this idea?
The geocentric model couldn’t explain retrograde motion.
Planets like Mars look like they drift from side to side.

5. Retrograde Motion

6. Heliocentric Model

7. New(ish) Ideas -- Brahe
Didn’t believe the heliocentric model
Stars should demonstrate parallax
Apparent shift in position

8. New(ish) Ideas -- Kepler
Developed 3 laws of planetary motion

9. Kepler’s 1st Law
Orbits are shaped like an ellipse with sun as one focus
Perihelion-closest to the sun
Aphelion- farthest from the sun
Major Axis
Minor (semi-major) axis
Keplers 1st Law

10. Ellipse

11. Ellipse

12. Kepler’s 2nd Law
A planet sweeps out an equal area in equal time no matter how fast it is moving.

13. Kepler’s 2nd Law

14. Kepler’s 3rd Law
The farther away a planet is from the sun, the longer it takes for one complete period.
1 astronomical unit (1 AU) is the average distance from sun to Earth

15. New(ish) Ideas -- Galileo
Created telescope
Observed Jupiter’s moons
Saw planets are spheres
Moon surface
Sun spots
House arrest

16. New(ish) Ideas -- Newton
Law of Universal Gravitation: Gravity keeps planets from flying away
Mass is proportional (Mass goes up, gravitational force goes up)
Longer the radius, weaker the gravitational pull.