Astronomy/Geology 1070: Earth: Its Physical Environment

Eighth Homework Assignment, Due December 1, 2011
20 points

Please submit your work to me by the beginning of class.

These questions are for you to combine different ideas and apply them to situations not directly addressed in class or in the textbook.  Think about the situation, and about the science that applies to it.  See me for help if you are stuck.

Do one, and only one, of the following:

1. Explain logarithms.

The Hertzsprung-Russell diagram has a “logarithmic” scale on both axes.  Explain what that means. Address in your explanation:

• the meaning of distance on a logarithmic scale
• why axis labels get closer together as they become larger
• the advantages of using a logarithmic scale for H-R diagrams.
 
2. Justify the main sequence.

When the luminosity (absolute magnitude) and spectral class (temperature) of most stars are plotted on a Hertzsprung-Russell diagram, they fall in a doubly-curved band, known as the “main sequence,” stretching from the upper left to the lower right of the diagram.  What does this tell astronomers about stars in general? What does it imply about the stars whose data do not fall on the “main sequence?”

3. Star types: pedagogic dialogue.

Write a dialogue between a college student and her six-year old niece as the college student explains why, although the stars all look about the same in the sky, astronomers know that there are different types of stars.

4. What galaxies are.

Galaxies had been observed at least as long ago as the Middle Ages, but not until Edwin hubble’s work was it known that they are “island universes” of stars vastly distant from our own Milky Way.  Explain what evidence was provided to prove this, and how it proves it.

5. Doppler shift: pedagogic dialogue.

A little boy and his mother are sitting on the front porch of their house when a fire truck rushes by.  The sound of the truck’s siren drops in pitch as the truck passes.  The boy asks, “Mommy, why did the fire truck change its noise when it went by?”  What does his mother tell him?  (Assume that she knows a lot about astrophysics.)

Take your choice of these tasks.  Do not submit answers to more than one of them.  Just choose one, and submit it.  Your answer should thoroughly address all points of the question.  An adequate answer will be several paragraphs long.

For the last time: Do not turn in paper that has ragged edges!  If you write your work in a spiral-bound notebook, trim the edge before submitting it.  Papers with ragged edges will be returned unmarked.  But you know that already.