1. Mr. Mac’s Earth Science Classroom Galaxies - Group of stars, gas, and dust. - There are over 40 billion galaxies in the universe! - 1000 to 1,000,000 light years wide.

2. Mr. Mac’s Earth Science Classroom New Vocab Worddddd…. Light Year (ly): distance light travels in one year. A light year is not a measure of time. Light travels 9.5 trillion kilometers in one year. That’s a lot! Star: 4.3 ly away  It will take light 4.3 years to reach our eyes. (Proxima Centauri)

3. Mr. Mac’s Earth Science Classroom What is a galaxy? There are three major types of galaxies: Spiral GalaxiesElliptical GalaxiesIrregular Galaxies.

4. Mr. Mac’s Earth Science Classroom Spiral Galaxies Pinwheel Shape Spiral Arms lots of gas/dust Central Bulge little gas/dust Halo of old stars Rotation

5. Mr. Mac’s Earth Science Classroom Elliptical Galaxies Ball shaped Very little gas/dust Most are very tiny Halo of old stars Mostly old stars

6. Mr. Mac’s Earth Science Classroom Elliptical Galaxies

7. Mr. Mac’s Earth Science Classroom Irregular Galaxies D. Hunter (Lowell Observatory), Z. Levay (STScI) Irregular Shape Lots of gas and dust Lots of stars forming Active and Volatile Conditions

8. Mr. Mac’s Earth Science Classroom Irregular Galaxies These galaxies are not spiral or elliptical. They are irregularly shaped. They contain lots of gas and dust which means that lots of stars are forming. D. Hunter (Lowell Observatory), Z. Levay (STScI) Local Group Galaxies Survey Team, NOAO, AURA, NSF

9. Mr. Mac’s Earth Science Classroom The Milky Way “face-on”  view “edge-on” (looking from the edge)  view 25 kpc = 25 kiloparsecs = 25,000 parsecs 75,000 light-years 8.5 kpc (2/3 of the way out)

10. Mr. Mac’s Earth Science Classroom The Big Bang Theory: 10 billion to 20 billion years ago: An expansion of space from a single point..

11. Mr. Mac’s Earth Science Classroom The Big Bang Theory: 10 billion to 20 billion years ago: Over time the universe has cooled, but is still expanding today. (What proof do we have? Stay Tuned!) … After about 1 billion years, the first stars and galaxies started to form…. The galaxies are expanding WITH space!!!

12. The Big Bang Theory: 10 billion to 20 billion years ago: Galaxies are moving with space not through it. The are in fixed positions. Getting farther apart from one another. There is no center or edges to the universe. Think of rasin bread…..

13. Mr. Mac’s Earth Science Classroom The Big Bang Theory: 10 billion to 20 billion years ago: The “raisin bread” analogy raisins  galaxies, dough  space

14. Mr. Mac’s Earth Science Classroom The Big Bang Theory: 10 billion to 20 billion years ago: The “raisin bread” analogy raisins  galaxies, dough  space

15. Mr. Mac’s Earth Science Classroom The Big Bang Theory: 10 billion to 20 billion years ago: The “raisin bread” analogy raisins  galaxies, dough  space Note: raisins are not moving through dough. Rather, blobs of dough are expanding, and pushing the raisins farther apart. Note: galaxies are not moving through space. Rather, blobs of space are expanding, and pushing the galaxies farther apart.