Pathways to Astronomy

Stephen E. Schneider

Chapter 69 Star Clusters - all with Video Answers

Educators

Chapter Questions

Problem 1

Sketch an H-R diagram for three clusters of stars. Make your sketches for one that is $10^{8}$ years old, one that is $10^{9}$ years old, and one that is $10^{10}$ years old. In what parts of the diagrams is the distribution of stars similar? in which parts is it different? Explain what causes the differences.

Sarah Mccrumb

Numerade Educator

02:17

Problem 2

We can see associations of $\mathrm{O}$ and $\mathrm{B}$ stars in the Andromeda Galaxy, 2 million ly away. What would be the brightness of an association of $70 \mathrm{O}$ stars at this distance?

Zachary Warner

Numerade Educator

01:48

Problem 3

The Hyades is 150 ly away from Earth, and is 75 ly in diameter. The globular cluster Omega Centauri is 18,000 ly away from Earth, and is 200 ly in diameter. What are the angular diameters of these two objects as seen from Earth?

Khoobchandra Agrawal

Numerade Educator

01:48

Problem 4

A globular cluster contains no main-sequence stars with surface temperatures higher than $5000 \mathrm{K}$ and luminosities greater than $0.80 L_{\odot} .$ How old is the cluster?

Donald Albin

Numerade Educator

06:07

Problem 5

If a globular cluster contains 1 million stars in a volume with a radius of 100 ly, what is the average separation between stars? Calculate this by assuming that each star fills one millionth of the total volume of the cluster. The diameter of the sphere it occupies is then the average separation. (The volume of a sphere is $4 / 3 \pi R^{3}$.)

Donald Albin

Numerade Educator

02:58

Problem 6

Suppose we were observing the globular cluster in problem 5 through a telescope. At the distance of the globular cluster, its radius appears to be 100 arcsec, so it covers an area on the night sky of $\pi \times(100 \text { arcsec })^{2}$
a. Supposing each star has the radius of the Sun, what is its radius in arc seconds?
b. What fraction of the area of the globular cluster is covered by the summed area of the million stars?

Prabhu Ramji

Numerade Educator