Astr 421 Fall 2004

Galaxies Sylvain Veilleux

October 6, 2004 DUE: October 15, 2004

**Problems 1 - 4.**

Sparke & Gallagher, Problems 3.2, 3.3, 3.6, and 3.19

**Problem 5.**

Assume that the Sun is in the midplane of the Galaxy with a vertical component of motion equal to 7 km s. Assume that the Sun moves through a constant-density region with = 0.13 M pc.

- (a)
- Apply Gauss's law in a plane-parallel layer to show that the Sun
executes simple harmonic motion with a force constant proportional to
.
- (b)
- Estimate the maximum height above the plane that the Sun will
reach.
- (c)
- In light of the derived value of z, is the assumption
of a constant density medium realistic?
- (d)
- Roughly how many vertical oscillations has the Sun made during its
lifetime (4.6 billion years)?

Sylvain Veilleux 2004-10-05