1. Lecture 34 – Galaxies and the Universe
Repeatedly said there are other galaxies. Now details
Large Magellanic Cloud (satellite to Milky Way) . Distance=50 kpc. Pic:
M31: Distance=730 kpc, Pic:
M33: Distance = 670 kpc, Pic:

2. These are the closest galaxies
Question: How do we know their distances?

3. Our Galactic Neighborhood- The Local Group
Galaxies come in clusters, too
A new unit, the Megaparsec

5. Beyond the Local Group Other small groups of galaxies
Typical spacing of a few Megaparsecs
Our “neighbors” include some of the brightest binocular galaxies
See Appendix 15 for list

6. Spirals, Ellipticals, Irregulars
Types of Galaxies
Spirals, Ellipticals, Irregulars

7. The Larger Neighborhood

8. The Virgo Cluster Distance ~ 20 Megaparsecs > 1000 galaxies
Largest are giant ellipticals like M87

10. Not the end of the story: the Abell clusters
Published in 1958
2718 “Rich Clusters” like the Virgo cluster
Most distant 2 billion light years

11. The Abell Clusters

12. Now the question: how can you know the distances to these objects?
You can’t see Cepheids that far out

13. Turn to one of Hubble’s greatest discoveries
He discovered galaxies as “island universes”
Measured distances to galaxies
Measured velocities (toward us or away)
How?

14. Illustration of a galactic redshift

15. The Hubble Relation for Galaxies
Galaxies in all directions receding from us
The more distant they are, the faster they are receding
v=H0d
v = speed of recession (km/sec), d= distance (Mpc), H0 “Hubble Constant”, (km/sec/Mpc), H0 = 70 km/sec/Mpc

16. The Hubble Relation for Galaxies
If you measure the redshift, you know the distance

17. With measurements of distances, you can map out the distribution of galaxies