1. Ch. 20 and 21

2.  Our solar system has been here for awhile  5 billion years!  It formed from a solar nebula  Clouds of dust in space that combined  Contain hydrogen and helium  Gravity formed it  Pulled everything together  Pressure makes sure it doesn’t collapse

3.  Took 10 million years to form  Flattened into a disk shape  This lead to the orbits of planets  Particles of dust started to collect together  Formed planetesimals (small planets)  Eventually gases go too hot near the center  Earth, Venus, Mars, Mercury  Farther out gases were cool  Jupiter, Saturn, Uranus, Neptune

4.  Dense gas in middle of nebula got so hot that…  Fusion began  Star was born (Sun)

5.  The sun is what keeps us alive  The Sun is a big furnace heating Earth  The Sun does not have a solid outside  The core is very dense but the outside is made of gas

6.  Many Theories:  1.) Shrinking sun (gravity gives off energy)  2.) Burning a fuel source  3.) Fusion (Correct Theory)  Albert Einstein, E=mc 2  2 hydrogen = 1 helium  This fusion gives us the layers of the sun

7.  The Sun is ever-changing  Sunspots:  Cooler, dark spots of the photosphere of the Sun  The number of Sunspots changes cyclically  About 11 years  They can even lower Earth’s temp.  Solar Flares:  Regions of extreme temperature  Extend thousands of miles into space  Disrupt communications on Earth

8.  Brahe started it  Kepler finished it  What did these two start?  Planetary Motions:  Each planet rotates on its axis  Each planet revolves around another object  How long does it take Earth to complete its revolution around the sun?  How about Mercury?  How do we determine time? 88 days!!!

9.  Studied planetary motion  Developed 3 laws:  1.) Planets revolved in an ellipse, not a perfect circle  2.) Planets move faster closer to the sun, slower farther away  Think of the Sizzler at the fair  3.) The farther or closer you are the sun will affect your revolving rate (Like weights in a chair)

10.  Newton explained the effects of Gravity  Gravity depends on the masses  distance  Law of Universal Gravitation  Ex.) 2 objects, 2 times farther away  Will have 4 times less gravity  Also explain why the moon falls down & around Earth (orbit + gravity)

11.  Planets:  “wanderers” in Greek  Our Solar system has 8  Each planet may have moons  Earth-1  Saturn-Dozens

12.  In space we use: Astronomical Units (AU)  1 AU= Distance between Sun and Earth  1 AU=8.3 Light Minutes  So how far apart are the other planets then?  To the hallway fellow scientists!

13.  Luna is Earth’s moon  Lunar Landing  Came about from a meteor striking Earth

14.  Moon goes through phases  Waxing = larger  Waning = smaller

15.  2 types:  1.) Lunar:  Earth between sun and moon  Shadow falls on part of moon  2.) Solar:  Moon comes between Earth and Sun  Shadow falls on Earth

16.  Comets :  Small body of ice, rock, and dust  Ex.) Shoemaker-Levy 9 collided with Jupiter  Asteroids :  Rocky bodies that revolve around the sun  Most occur in Asteroid belt between Mars and Jupiter  Meteoroid :  Similar to asteroids but smaller  Meteorite -hits Earth, Meteor - bright streak in sky