1. Chapter 23
The Solar System

2. Models of the solar system
Earth-centered
Geocentric model
First model, held as true for a very long time; Earth is center of universe and other planets revolve around it
Ptolemy proposed it
Stars, moon, sun appear to move as the day goes on

3. Models of the solar system
Sun-centered
Heliocentric model
Nikolas Copernicus proposed and presented a model
Galileo provided evidence for it when he discovered moons around Jupiter and phases of Venus
Johannes Kepler expanded on the idea and proved that planets move in ellipses, not perfect circles

4. Models of the solar system
Kepler also discovered that planets travel at different speeds (closer to the sun travel faster than planets further from the sun; outer planetrs take longer to orbit than inner planets
Inner planets: Mercury, Venus, Earth, Mars
Outer planets: Jupiter, Saturn, Uranus, Neptune (Pluto considered an outer dwarf planet)

5. Formation of the solar system
Nebular Hypothesis
Nebula—big ball of gas
Left over from exploded stars

6. Formation of the solar system
Starts as a large ball of slowly spinning dust
Gravity causes it to clump in the center
As it contracts, it spins faster (just like an ice skater)
As it spins faster, it flattens

7. Formation of the solar system
As it grows more dense in the center, it heats up
Once it reaches about 10 million degrees, nuclear fusion starts, forming a star at the center
Fusion is just when small atoms hit each other fast enough and hard enough to stick, releasing lots of heat and light

8. Formation of the solar system
Most of the mass of the solar system is in the sun
Remaining mass clumped together to form planets, asteroids, and comets as they cooled
Closest planets are made of the heaviest elements (rocky)
Farther planets are made of lighter elements (gaseous)
Farthest objects are mostly ice

9. Comets Comets— dust and rock mixed with frozen water
Very eccentric orbits
When they come close to sun, ice evaporates and forms a tail
Tail is pushed directly away from the sun
Halley’s Comet
Comet Hale-Bopp

10. Meteors Meteoroids—small pieces of rock from old comets
When they enter the atmosphere, they start to glow and burn
Meteors—meteoroids that burn up completely
Meteorites—meteoroids that reach the surface
Meteor Crater, Arizona

11. Asteroids Asteroids—rocks similar to the material in the planets
Not large enough to be made into a ball due to its own gravity, like a planet
Most exist between Mars and Jupiter, in the asteroid belt