Activity 25: RR Lyrae Stars and the Distance to
the Center of the Galaxy
©2014 W.W.Norton &Company, Inc.
15
Post-25.1: What aspect about globular clusters and our
observations of the distances to them modified our view
of the Milky Way Galaxy and our place in it?
a. They all orbit the center of the galaxy, and the center
of their distribution is not where we are.
b. Some of the globular clusters are very far away and
must belong to the Andromeda Galaxy.
c. We found out that there are hundreds of globular
clusters hidden by columns of dust.
d. The most distant globular clusters are metal-rich and
so must have originated in the disk.
©2014 W.W.Norton &Company, Inc.
16
Post-25.1: What aspect about globular clusters and our
observations of the distances to them modified our view
of the Milky Way Galaxy and our place in it?
a. They all orbit the center of the galaxy, and the
center of their distribution is not where we are.
b. Some of the globular clusters are very far away and
must belong to the Andromeda Galaxy.
c. We found out that there are hundreds of globular
clusters hidden by columns of dust.
d. The most distant globular clusters are metal-rich and
so must have originated in the disk.
©2014 W.W.Norton &Company, Inc.
17
Post-25.2: Astronomers need to measure the distances
to the stars in the Milky Way globular clusters.
What method should they use to find the distances?
a. Measure the trigonometric parallaxes of all the
globular clusters during the course of a year.
b. Count the number of O- and B-type stars and
remnants of supernovae in the clusters.
c. Look for flickering X-rays coming from black holes
in binary systems in the clusters.
d. Find RR Lyrae variable stars in the clusters and
measure their mean apparent magnitudes.
©2014 W.W.Norton &Company, Inc.
18
Post-25.2: Astronomers need to measure the distances
to the stars in the Milky Way globular clusters.
What method should they use to find the distances?
a. Measure the trigonometric parallaxes of all the
globular clusters during the course of a year.
b. Count the number of O- and B-type stars and
remnants of supernovae in the clusters.
c. Look for flickering X-rays coming from black holes
in binary systems in the clusters.
d. Find RR Lyrae variable stars in the clusters and
measure their mean apparent magnitudes.
©2014 W.W.Norton &Company, Inc.
19
Post-25.3: Why are globular clusters ideal for
determining the size of the Milky Way and our location
in the galaxy?
a. Most lie above the plane of the Milky Way and
so are not very obscured by dust.
b. Most globular clusters have a large number of
RR Lyrae variable stars.
c. The clusters must orbit the center of the galaxy.
d. All of these answers are correct.
©2014 W.W.Norton &Company, Inc.
20
Post-25.3: Why are globular clusters ideal for
determining the size of the Milky Way and our location
in the galaxy?
a. Most lie above the plane of the Milky Way and
so are not very obscured by dust.
b. Most globular clusters have a large number of
RR Lyrae variable stars.
c. The clusters must orbit the center of the galaxy.
d. All of these answers are correct.
©2014 W.W.Norton &Company, Inc.
21
Post-25.4: An observer far outside our galaxy would
best describe our galaxy and the Sun's position in it as a
a. disk of stars with our Solar System toward the
edge.
b. disk of stars centered on our Solar System.
c. disk of stars with our Solar System located in the
bulge.
d. sphere of stars centered on our Solar System.
©2014 W.W.Norton &Company, Inc.
22
Post-25.4: An observer far outside our galaxy would
best describe our galaxy and the Sun's position in it as a
a. disk of stars with our Solar System toward the
edge.
b. disk of stars centered on our Solar System.
c. disk of stars with our Solar System located in the
bulge.
d. sphere of stars centered on our Solar System.
©2014 W.W.Norton &Company, Inc.
23
This concludes Activity 25: RR Lyrae Stars and
the Distance to the Center of the Galaxy
©2014 W.W.Norton &Company, Inc.
24