1. Today’s Agenda…
Bellringer: How are comets and meteorites different? Which one do we refer to as a shooting star?
Review yesterday’s topics
Notes on Galaxies and the Universe

2. Today’s goals…

3. Galaxies and the Universe
Study Pack #12

4. What is a galaxy?
A galaxy is a group of stars, gas, and dust held together by gravity
Different shapes and sizes

5. Types of Galaxies Elliptical Spiral Irregular Named for their shape
Page 460

6. The Milky Way Galaxy Spiral galaxy Hundreds of billions of stars
Everything revolves around the center of the galaxy including the sun
Figure 26 – Why is it called the Milky Way galaxy?

7. The Universe As many as 100 billion galaxies might exist
All of the galaxies with all their stars make up the universe
Page 463, Figure 28 – hundreds of galaxies in one part of the sky
Think about how small Earth is in comparison to the universe!!!!

8. Measuring in Space Astronomical Unit
Can measure distances between planets
Equals 150 million kilometers (average distance form the sun to the Earth)
Abbreviated AU
If something is 3 AU away from the Sun it is 3 times farther from the sun than Earth is

9. Measuring in Space Light Years Can measure distances between galaxies
It is the distance light travels in one year, about 9.5 trillion kilometers
Page 462

10. Assignment….
Page 468
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