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Conceptual Questions



1

The Sun is actually much less luminous than Sirius. What effect does this fact have on the accuracy of Newton's determination of the distance of Sirius?
2

Both parallax and proper motion are changes in the apparent positions of stars. Describe how observations carried out over many years could be used to distinguish the changes caused by parallax from those due to proper motion.
3

Suppose the Sun moved through space much faster than it actually does. What effect would this have on the directions of the apex and antapex of the Sun's motion? What effect would this have on the sizes of the proper motions of nearby stars?
4

Explain why the absorption lines of an element have the same wavelengths as the emission lines of that element.
5

Why is it impossible for a gas composed of atoms that all have their electrons in the ground state to produce an emission line?
6

Make up your own mnemonic to help you remember the sequence of spectral classes.
7

Why are Balmer lines weaker in the spectra of O stars than they are in the spectra of A stars?
8

Why are Balmer lines weaker in the spectra of G stars than they are in the spectra of A stars?
9

What can be said about the radial velocity of a star that shows no Doppler shift of its spectral lines?
10

Which of the following pairs of quantities can be plotted against each other to produce an H-R diagram? (a) temperature and distance (b) luminosity and spectral class (c) temperature and spectral class (d) radial velocity and apparent magnitude
11

What is the reason that most of the stars in an H-R diagram, such as Figure 16.20, are located on the main sequence?
12

How does the brightness of a giant star compare with the brightness of a main-sequence star of the same spectral class?





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