The HR Daigram Lab

The lab manual write-up is pretty complete on this exercise and watching the 
lab prep will fill in most gaps in the procedure, so I think I can be brief.

There is quite a bit of graphing in this exercise.  Be careful in plotting the
Absolute magnitudes.  Recall that magnitude is an inverted scale.  We want the
brighter objects higher on the graph (just like the text), but those brighter
stars correspond to smaller absolute magnitudes.  A 1.0 magnitude star is brighter
than one of magnitude 1.1, so the 1.0 star is higher on the graph.  This is a
bit confusing at first and you have to keep reminding yourself.

We start by graphing Table 3 onto Figure 1.  Put M on the vertical scale, spectral
type on the horizontal scale.  I picked stars that would nicely define the Main
Sequence.  Make this plot accurate since we will transfer the Main Sequence that
you draw here onto each of the other graphs.

I make the argument for luminosity associations with stellar radius in the lab
prep and also in the lecture on the HR Diagram, so you may want to review that lecture.

Now you're ready for the work of the lab - plot Table 6 onto Figure 2 and Table 7
onto Figure 3.  The first are the bright stars, the second are the nearby stars.
I hope you will see a marked difference in their distributions on the HR Diagram.
We hope that the nearby stars represent an average distribution of stars in the sky.
Did you get the result that the average star is too faint to be seen without a telescope?
Hipparchus chose bright stars in trying to search for stellar parallax.  Was this
a wise choice?

How good are you at making graphs using a spreadsheet?  I simply imported the tabular
values in EXCEL and made my graphs there.  If this doesn't intimidate you - go for it.
Just make sure to make your scales agree with those in the lab manual.  Not familiar
with graphing in EXCEL?  Now is not the week to learn!

Question 10 requires some thought.  If every star were like the Sun (M = 5) what
would the sky look like?  Notice that the Sun is a little brighter than the average
star.  But also notice that it is considerably fainter than the list of bright stars.
If all those bright stars were like the Sun, would we see them?  The Millky Way is
the combined glow of the stars of our galaxy (300 billion or more).  What would the
Milky Way look like?  If the nearby stars were like the Sun, how would their appearance
change?  There's a lot to think about in this question.