1. Announcements Third exam is Friday, October 29
Review on Wednesday, October 27
Please hand in or questions for the review

2. Cosmic Distances How to measure distances Primary distance indicators
Secondary and tertiary distance indicators
Recession of galaxies
Expansion of the Universe

3. Stellar Parallax
As the Earth moves from one side of the Sun to the other, a nearby star will seem to change its position relative to the distant background stars.
d = 1 / p
d = distance to nearby star in parsecs
p = parallax angle of that star in arcseconds

4. Stellar Parallax
Most accurate parallax measurements are from the European Space Agency’s Hipparcos mission.
Hipparcos could measure parallax as small as arcseconds or distances as large as 1000 pc.
How to find distance to objects farther than 1000 pc?

5. Flux and Luminosity
Flux decreases as we get farther from the star – like 1/distance2
Mathematically, if we have two stars A and B

7. Standard Candles

8. Standard Candles Measure the distance to star A to be 200 pc.
Measure the flux of star A.
Measure the flux of star B with same spectral type and luminosity class to be lower by a factor of 1600
Find the distance to star B

9. Distances to galaxies
Standard candles, such as Cepheid variables, the most luminous supergiants, globular clusters, H II regions, and supernovae in a galaxy, are used in estimating intergalactic distances.

10. The Distance Ladder
Each stage in the ladder overlaps the previous and next
Cepheid distances are critical
Tully-Fisher, fundamental plane apply to whole galaxies
Supernova are now the best estimators at large distances

11. Distances and velocities of galaxies
If you measure the distances to a large set of galaxies and also measure the speed of the galaxies using the redshift, what do you find?

12. Hubble expansion v = H0d

13. Expansion of the Universe

14. Expansion of the Universe
Blow up the balloon to about a 3 inch diameter. Twist the neck and hold it closed so that no air escapes, but do NOT make a knot because you will need to blow it up some more. Make SIX dots on its surface to represent galaxies and label them A-F.
Measure and record the distances from cluster A to each of the other 5 clusters.
Measure and record the distances from cluster D to each of the other 5 clusters.
Blow up the balloon up more, to a diameter of about 6 inches. Measure the distances between the same clusters again and record them.

15. Expansion of the Universe
Are all the other clusters moving away from cluster A?
Are all the other clusters moving away from cluster D?
Is there a cluster that could be considered to be at the center of the universe as represented by the surface of the balloon?