Chapter 16

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.

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?

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

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

Why are Balmer lines weaker in the spectra of \(\mathrm{O}\) stars than they are in the spectra of A stars?

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

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

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

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