•Q1. 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, star B has a period of 18 days. Which is closer to
Earth?
–Faster
varying variables are less luminous, therefore Star A is less luminous than B.
Therefore
if Star A appears as bright from Earth as B, it must be closer.
•Q2. Which of the following is not a characteristic of
the stars of the disk component
of our galaxy?
–Randomly
inclined orbits
•Q3. If all the mass in our galaxy were centrally
concentrated, we'd expect velocities
to fall with increasing distance according to Kepler's laws. This is not seen in the disks of spiral galaxies. Galactic
rotation curves appear "flat" with increasing distance. This must be due to:
–The
gravitaional influence of "dark matter" in the halo.
•Q4. If
the sun is 5 billion years old, how many times has it orbited the galaxy? Assume a circular orbit for the sun.
–Need
velocity of the sun (about 220 km/s) and the orbital circumference (2πr), where r=8.
5kpc. Number of orbits in 5
billion years is then 5 billion years/time for one orbit,
which is circumference/220 km/s.
Converting units gives an orbital period of 240
million years. Therefore in 5
billion years the sun has orbited about 21 times.
•Q5. If interstellar dust makes and RR Lyrae star look
1 magnitude fainter than it
should, by how much will we overestimate its distance?
–Star
looks 1 mag fainter. Distance = 10
(m-M+5)/5 so our estimate will
differ by a factor of 101/5 which is about 1.6.
•