Astronomy 100 - Problem Set 7
Due: Thursday 24 April 2008
Name:

Fill in the box with the correct answer (answers should be just a few words or a number).

  1. What is the diameter of the Milky Way Galaxy in which we live. To appreciate the scale, express your answer in AU (astronomical units = the distance between the Earth and Sun = 150 million kilometers) and note that it takes a spacecraft about a year to travel an AU.

  2. One can make a more general version of Kepler's Third Law which accounts for the mass of the object being orbited

    M P2 = a3

    Everything works if P is expressed in years, a is expressed in astronomical units (AU), and M is in units of the Sun's mass (so in the Solar System M=1). You can apply this equation to an entire galaxy of stars, in which case you measure the mass which lies interior to the orbit of the star for which you know "a" and "P".

    In the last problem you determined the Milky Way Galaxy diameter in AU. The Sun orbits the center of the Galaxy at a distance of a=2x109AU. It takes roughly P=200 million years for the Sun to complete an orbit around the center. How much mass does the Milky Way contain inside the Sun's orbit?

  3. What (approximately) would the period of variation be for a classical Cepheid star that has a luminosity 10,000 times that of the sun according to Figure 12-14?

  4. Approximately what is the spectral type of the star in the question above?

  5. Put in order from least number of stars to most:

    A. Globular Cluster
    B. Galaxy
    C. Open Cluster

  6. Which of the following objects is likely to contain the oldest stars: a Galactic (open) Cluster, a Globular Cluster, or a Molecular Cloud?

  7. (2 points) Describe the differences between globular and galactic open star clusters. How do their histories and environments differ? Sketch an edge-on view of our Galaxy. Indicate the location where Globular and Galactic open clusters are found.