WHAT IS THE MILKY WAY?WHERE ARE WE IN THE MILKY WAY? HOW DO WE KNOW?

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.

ARE WE IN THE MIDDLE? HOW WOULD THINGS LOOK IF WE WERE?

ARE WE ARE WE ON THE EDGE? HOW WOULD THINGS LOOK IF WE WERE?

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

WHERE IS THE BRIGHTEST AREA?WHY IS IT BRIGHTER THAN OTHER AREAS IN THE SKY?

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.

Side view Sketch this diagram of our Milky Way galaxy saucer

Our Sun lies on the disk

Thin part: disk

OUR CLOSEST NEIGHBORWe 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?

Locating Andromeda Galaxy in the night sky.

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.

https://www.youtube.com/watch?v=4ffI0l8vUK8 gravity well

• The balls on the outside move slower, the balls near the center move faster.

Disk of gas and stars rotates about galactic centerDifferential rotation: the stars in the disk rotates at different speedsDifferential 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

MILKY WAY STORY SO FAR… 1. Billions of stars

2. Spiral galaxy: distinct arms

3. Shape is a flat disk

4. We’re not at the center, 2/3 way from center

5. It rotates (differentially) once in 225 million yrs.

6. Center (bulge) appears near the constellation Sagittarius

9. It contains halo of interstellar gas, stars

10. 100,000 light years across x 10,000 ly thickhttps://www.youtube.com/watch?v=oWKJAmOIZlQ NASA 10 facts

http://list25.com/25-crazy-facts-about-the-universe/ 25 crazy facts