Measuring the Universe: The Distance Ladder: Practice Problem Solutions

1. No single method works at all distances. Each works over a limited range and is calibrated by the previous one.

2. An object whose true brightness is known, so that its apparent brightness gives its distance.

3. Its pulse period tells its true brightness (longer period, brighter star). Comparing that with how bright it looks gives its distance.

4. m − M = 19.3 − (−19.3) = 38.6.

5. They all peak at nearly the same true brightness and are so bright that they can be seen billions of light-years away.

6. He found Cepheids in Andromeda and used Leavitt's relation to show that it was far outside the Milky Way.

7. Each rung is calibrated by the one below it, so an error at the bottom carries up to all the higher rungs.