1. What is the Milky Way? WHERE ARE WE IN THE MILKY WAY? How do we know?
Every star you can see is one of a billions of stars randomly scattered in the sky except for the bright diagonal band of stars. Looks like smoke, milk, steam? Because we can see these stars, we know we are a part of the same system (Galaxy)

2. Are you in the middle of the forest. Or near the edge. What is UP
Are you in the middle of the forest? Or near the edge? What is UP? Which direction is out? Stand up in your seat – your class is like a forest.
Diagram in your notebooks or an a white board what a 360 degree view would look like. Use dots for the trees. What would you see looking UP?

3. Are we in the middle? How would things look if we were?
Every star you can see is one of a billions of stars randomly scattered in the sky except for the bright diagonal band of stars. Looks like smoke, milk, steam? Because we can see these stars, we know we are a part of the same system (Galaxy)

4. Are we Are we on the edge? How would things look if we were?
Every star you can see is one of a billions of stars randomly scattered in the sky except for the bright diagonal band of stars. Looks like smoke, milk, steam? Because we can see these stars, we know we are a part of the same system (Galaxy)

5. The shape of the milky way
In the late 18th century, William Herschel proposed that the Milky Way Galaxy was a flat disk shape
He claimed we were toward the center

6. Where is the brightest area
Where is the brightest area? why is it brighter than other areas in the sky?
Every star you can see is one of a billions of stars randomly scattered in the sky except for the bright diagonal band of stars. Looks like smoke, milk, steam? Because we can see these stars, we know we are a part of the same system (Galaxy)

7. How the Milky Way got its name
The bright band across the night sky consists of billions of bright stars.
It is named because it looked like milk pouring out of
(or steam rising from)
the teapot of
the constellation
Sagittarius.

8. We see fewer stars in all directions except when we are looking through the center and all the way across the galaxy

9. Side view Sketch this diagram of our Milky Way galaxy saucer
Our Sun lies on the disk
Thin part: disk
A side view (profile) of our galaxy

10. How would you describe it’s shape?
Our Closest Neighbor
We can’t see our own galaxy, so we look at other galaxies similar to our own to predict behavior
The Andromeda Galaxy is our closest neighbor at 2 million ly away
Only galaxy outside our own galaxy that is visible with the naked eye
How would you describe it’s shape?

11. Locating Andromeda Galaxy in the night sky.

12. Our Sun (one of a billion stars in the Milky Way), and our solar system is located NOT in the center, and NOT at the edge, but about 2/3 out on a spiral arm.
You can stop here if you don’t want to discuss differential rotation which explains the SPIRAL arms of the galaxy.

13. Outer ball moves slower and the inner ball moves faster just like the stars in the Milky Way are rotating around the center of the galaxy
The balls on the outside move slower, the balls near the center move faster.
gravity well

14. Disk of gas and stars rotates about galactic center Differential rotation: the stars in the disk rotates at different speeds Differential rotation causes the inner stars to rotate faster – passing the outer cloud which is moving slower, so they lag behind. This causes the spiral arms of the galaxy

15. Milky Way story so far… Billions of stars Spiral galaxy: distinct arms
Shape is a flat disk
We’re not at the center, 2/3 way from center
It rotates (differentially) once in 225 million yrs.
Center (bulge) appears near the constellation Sagittarius
It contains halo of interstellar gas, stars
100,000 light years across x 10,000 ly thick
NASA 10 facts
crazy facts