3. Read pp. 646-648 Fill in your Cornell notes about galaxies!

4. distant galaxies as seen by Hubble (Get out your cornell notes)

5. Galaxy – collection of stars, dust, and gas held together by gravity 3 types Spiral - whirlpool shape, classified by bulge size ( middle) young blue stars – around middle old stars- in the bulge sun like stars- in the arms Elliptical football shape- old stars, little gas or dust Irregular smaller shape, hot gas and dust mostly younger stars

6. Hubble Tuning Fork Diagram

7. Milky Way Galaxy 100,000 light years 300 billion stars

8. Irregular IC 1613 spiral (M51 Whirlpool) elliptical (M87 Virgo A)

9. Hubble Space Telescope Launched in 1990 Outside atmosphere for clear photos $1.5 BILLION First images were fuzzy! Mirror was wrong shape… too flat by a few nanometers Astronauts had to go up and install a corrective lens

10. Galaxy M100 photos before & after Hubble mirror adjustment

11. Sloan Digital Sky Telescope http://www.sdss.org/education/#for- educatorshttp://www.sdss.org/education/#for- educators

12. M31 The Andromeda Galaxy 1. Andromeda is about 2.3 million light years away, making it the nearest major galaxy to our own. (Other smaller galaxies have been discovered only recently, because they had been hidden by dust from the Milky Way. The closest known galaxy to us is the Canis Major Dwarf Galaxy, at 236,000,000,000,000,000 km (25,000 light years) away.) 2. Andromeda is also the most distant object visible to the naked eye. 3. Astronomers estimate the mass of Andromeda at over 300 billion suns. This is almost twice as massive as our own Milky Way galaxy.

13. How many galaxies in the universe? 125-500 billion How are galaxies formed? (several theories) 1. after big bang stars formed clusters and teamed up to stars, clusters, then galaxies 2. One big clump after big bang and matter started to divide.

14. Why classify and study them?