1.  At one time, the universe was a dense, hot, supermassive ball.  About 13.7 billion years ago, a violent explosion occurred sending material in all directions into space.

2. This marked the beginning of the universe. Eventually, matter cooled and condensed into galaxies, stars, and planets.

3.  Red shifts  Cosmic background radiation  Radio signals coming from every direction in space.  Believed to be created by the big bang explosion.

4.  1929 – Edwin Hubble found that the universe is expanding  Estimated distances, relative brightness, Doppler red shifts

5. Dimmer galaxies had greater red shifts  farthest from Earth and moving faster Hubble’s Law: the more distant the galaxy, the greater the red shift- they are moving away at faster speeds.

6.  A cloud of dust gas (nebula) created the planets in our solar system.

7. A. Cloud of dust and gases (mostly hydrogen and helium) B. Started rotating and collapsing toward the center C. Rocky and metallic materials form as nebula cools

8. D. Collisions of particles created asteroid-sized objects E. Asteroids combined to form planets (Mercury, Venus, Earth, Mars); gases and lighter particles formed planets farther from the center (Jupiter, Saturn, Uranus, Neptune)

9. Nebula= cloud of dust and gas (HYDROGEN)  Protostar : gravity draws gas in nebula together  Collisions between atoms become more frequent  gases heat up.  Temperatures above 15,000,000 C  Hydrogen atoms combine in nuclear fusion to form Helium  Light is produced  new star is born

10.  Protostar: growing nebula  Main sequence: nuclear fusion combines hydrogen in core into helium (Stars will remain in this life stage for billions of years)  Red giant: hydrogen fusion moves outward from core, causing star to increase in size and decrease in temperature

11.  Rotation  spinning of Earth from west to east  results in day and night  Earth makes a complete rotation in 24 hours

12. Revolution Earth moves around the sun (elliptical) every 365¼ days Perihelion – Earth is closest to the sun Aphelion – Earth is farthest from the sun Precession Change in Earth’s axis very slow movement

14.  Earth’s axis is tilted 23.5 o  March 20/21 – Spring Equinox (#4)  June 21/22 – Summer Solstice (#1)  September 22/23 – Autumn Equinox (#2)  December 21/22 – Winter Solstice (#3)

15.  The moon moves counterclockwise to Earth  Perigee – moon is closest to Earth  Apogee – moon is farthest from Earth  Phases of the moon are the different amounts of light that appears on the moon (see illustration)

16.  Occurs during full moon phases  Penumbra – light is partially blocked by Earth  Umbra – light is completely blocked by Earth

17.  Occurs when sun is blocked by the moon  If the moon is partially blocking the sun, a partial solar eclipse will occur

18.  Galaxies – billions of star groups  more than 100 billion galaxies, each containing billions of stars.