Astr 104, Spring 2008 – Quiz 5

1. Is it common for two stars to be so close that they orbit around each other?
a. No, stars do not orbit around each other, only planets orbit around stars.
b. No, only about 1% of stars are sufficiently close to each other.
c. Yes, possibly about half of all stars are that close to each other.
d. Yes, every star we know revolves around one or more other stars.

2. Which of these is not a good method to check if a certain star is actually a binary?
a. Look for small changes in the wavelength of its light.
b. Look for periodic changes in its brightness.
c. Locate a second, fainter star on a telescope image.
d. See what part of the HR diagram the star is located in.

3. Why does the wavelength of the spectral lines of some binary stars change in time?
a. Because the light from each star is deflected by the other star.
b. Because the stars move toward and away from us in their orbits.
c. Because binary stars are unstable and their size changes in time.
d. Because we have to keep moving our telescopes to follow the stars.

4. What fact makes binary stars particularly useful for astronomers?
a. Stars in binary systems move more, so we can find their distance more easily.
b. By measuring their orbits around each other, we can find the stars' masses.
c. Two stars together are brighter and easier to see than a single star would be.
d. Stars in binary systems have shorter lives, and we can watch what happens at the end.

5. Name two stars that are known to be binary stars.