Astronomy 10 Spring 2000

Worksheet #3

1. Calculate the angular size (in degrees) of your thumb’s width, held at arm’s length. Use the small angle formula: [angular size] = 57.3 degrees * [size of object] / [distance]. What is the angular height of a car seen 100m away? 1 km away?

What kind of object subtends 1 arcsec at a distance of 10km?

2. What is the phase of the moon during a total solar eclipse? Why is a total lunar eclipse visible everywhere the moon is visible, but a total solar eclipse is visible only in a narrow swath on the Earth? Why don’t we get eclipses every month?

3. What is the relative strength of the tides due to the Moon compared to those due to the Sun? Recall that tidal forces are inversely proportional to the cube of the distance. The ratio of the Sun’s mass to the Moon’s is about 3x10⁷, and the Sun is about 400 times further away.

4. Why does the Moon always present the same face to the Earth? Which way does the dark side of the Moon always face? What is the relation of the Earth-facing side to the dark side?