1. THE UNIVERSE

2. How it started...  THE BIG BANG THEORY  At one time everything was compacted together in an extremely small, dense, ball of energy, and then 10 – 15 billion years ago something caused it to EXPLODE.  Because of this, nebulas, stars, galaxies, planets and other bodies formed.  The universe is still EXPANDING today.

3. Components of the Universe  NEBULA  A large cloud of dust and gas where stars are born.

4. Components of the Universe  Stars  4 kinds of stars  White Dwarfs  Main Sequence – our Sun  Giants  SuperGiants  They are classified using their size and color.  Our Sun is a MEDIUM sized star that gives off a YELLOW color.

5. Stars  Use the H–R Diagram to classify the stars Spectral Class O B A F G K M

6. Things to remember about the H–R diagram  Hottest stars are BLUE  “Coldest” stars are RED  The Sun is Yellow  Oh Be A Fine Girl, Kiss Me – to remember spectral class Spectral Class O B A F G K M

7. Our Sun  The sun appears so large to us because it is the closest star to Earth.  It is many thousands of times closer to Earth than any other star.

8. Components of the Universe  GALAXIES  A large group of stars, solar systems, and gas and dust.  We live in the MILKY WAY Galaxy.

9. Galaxies  There are 3 types of galaxies...  Spiral Galaxy  Spiral shaped; Milky Way is a spiral galaxy  Elliptical Galaxy  Oval/Circular shaped; contains old stars  Irregular Galaxy  No obvious shape

10. Milky Way Galaxy  Our solar system is located on an outer arm of the galaxy.

11. Components of the Universe  Other celestial bodies...  Asteroids  Comets  Satellites  An artificial or natural body that revolves around another object in space.  Artificial satellite – Hubble Telescope  Natural satellite – The Moon

12. Light Years  The Universe is so large and galaxies and objects are so far apart that scientists use Light Years to measure distances between them.

13. Light Years  Speed of Light is 300,000 km/second  In 1 year, light can travel 9,500,000,000,000 km  OR 9.5 trillion km  The closest star to the sun is 4 light years away or 38,000,000,000,000 km away.