1. The Milky Way Galaxy

2. The Development of an HII Region--
HII regions are clouds with ionized hydrogen

3. Space is filled with interstellar gas and dust
Light hits the dust and can produce
1. Dark nebula (if blocks/scatters lots of light)
2. Emission nebula (if dust is close to stars--reddish)
3. Reflection nebula (if dust is far from stars--bluish)

4. Dark Nebula, Emission Nebula, Reflection Nebula

5. What can you see through dust?
Longer waves pass through easier
Lets infrared waves through gas and dust clouds (and 21 cm radiation)
Previous experiments about size and shape of the Milky Way were off because they didn’t account for interstellar gas and dust.

6. The Distribution of Globular
Clusters in the Galaxy

7. The Distribution of Globular Clusters in the Galaxy
Sun is 28,000 ly from the center
about 150 Globular Clusters in Milky Way
globular clusters are found in halo around galaxy
globular clusters contain redder, older stars
Spiral arms contain younger, bluer stars

8. The Galactic Coordinate System

10. Milky Way Basic Facts ~3,000 light years thick
~100,000 light years across
We are ~28,000 ly from the center
Contains ~200 billion stars
Total mass = 1x 1012 solar masses
spiral structure
Supermassive black hole of 2 1/2 million solar masses at center
Missing Mass = 90% (dark matter)
Q: How do we know there is dark matter?
A: From rotation rates…outside stars are spinning just about as fast as inside stars
What is dark matter?
A: there’s your nobel prize because we don’t know.

11. The Shape of the Milky Way

12. 21 cm Observation of Spiral Structure

13. Spiral Arms Near the Sun --plot of bright, young stars

14. Where would I look to look toward the center of the galaxy?
The center lies in the direction of the constellation Sagittarius (Sgr A*), but very close to the border of both neighbor constellations Scorpius and Ophiuchus.
Note…this is NOT the center of the universe, just our galaxy.

15. What do we see? (a panoramic view)