•Question 4 (1 point) The use of Cepheid
variable stars to find distances
relies on the fact that
a. their luminosities are related to their
ages. b. their luminosities are all the same. c. their radial velocities are related to
their periods. d. their luminosities are related to their
periods.
•
• Question
5 (1 point) You observe two Cepheid variable stars, A and B, which have the same average apparent
magnitude. Star A brightens
and dims with a period of 5 days, while star B has a period of 18 days. Which star is closer to
Earth?
a.Star A b.Star
B c.Star A and B are at the same distance d.You cannot tell from this information
•Make the
following argument to solve this one easily.
The period-luminosity
relationship is precise, but precision is not needed here. The star with the longer period will be
more luminous, so that is star B. But we want to
know the distance. They both appear to have the same average apparent
magnitude. If one is more luminous than the other, the more luminous
one must be farther way – if it wasn’t, it would appear brighter. Therefore the less luminous star is closer, and that is star
A.