Homework Assignment #11

Name:

Section number:

Date Due: Dec. 8

1. How would the Milky Way galaxy appear to an observer located (a) on a planet at the edge of the galaxy and (b) at the galactic nucleus?

2. What are the principal differences (e.g., age, color, and temperature) between open and globular star clusters?

3. The Sun moves in a circular orbit of radius 2.6 · 1017 km around the center of the Milky Way, and its orbital speed is about 220 km/s. [1 year = 3 · 107 s]

(a) How long does it take the Sun to complete one orbit around the galaxy, in years?

(b) From this figure, calculate the mass of the galaxy that lies inside the Sun's orbit. Express your final answer in solar masses.

4. The observed rotation curves of most spiral galaxies become flat at large radii from their centers. What can be inferred about the distribution of matter in these galaxies?

5. A Cepheid variable star in a nearby galaxy appears roughly 108 times fainter than an identical Cepheid observed in the Milky Way, whose distance is 1,000 parsecs. Using the inverse square law, calculate the distance to the nearby galaxy.

6. A distant galaxy has a recessional velocity of 25,000 km/s. If the value of Hubble's constant is 65 km/s/Mpc, what is the galaxy's distance in Mpc?