Our Place in the Galaxy: Practice Problem Solutions

1. About 26,000 light-years, in the Orion Spur (a minor arm).

2. About 230 km/s; about 225 million years for one orbit.

3. The disk of our galaxy seen edge-on from inside: we are looking along the plane at billions of faint stars.

4. In that direction we are looking toward the galaxy's center, where stars and clouds are thickest.

5. They orbit about as fast as stars closer in, which means there is much more mass than we can see (dark matter).

6. Two small irregular galaxies that orbit the Milky Way, about 160,000 and 200,000 light-years away.

7. About 4 centimeters across, the size of a large coin.