1.  In class we've shown how visible, ultraviolet, and infrared light could be produced by certain transitions in the hydrogen atom's energy level diagram. 

a) Can the hydrogen atom produce spectral lines at x-ray wavelengths?  If so, convince me how (perhaps by presenting a sample transition).  If not, be convincing as to why not.

b) Can the hydrogen atom produce spectral lines at radio wavelengths?  If so, convince me how (perhaps by presenting a sample transition).  If not, be convincing as to why not.

   2. Look at the spectra of various stars on page 423 in FK.  You will have noticed that the hydrogen lines are strong (i.e., dark) only in certain stars. 

a) Being naive (i.e., not having read section 19-5), what might be a reason for why hydrogen has strong dark lines in some stars but weak lines or no lines at all in other stars?

b) Now read section 19-5.  What's the real reason?

   3. a) What astrophysical objects that we encountered in the image processing lab produce their light by fluorescence (and therefore have a bright line spectrum) because they are transparent gases?  I believe that there are at least 5 -- maybe even 6, depending on how you count.

In each case, is the fluoresce excitation via absorption of UV light or via collisions (and an exchange of kinetic energy)?

b) Give 2 examples from the image processing lab where the spectrum would NOT have been bright-line or emission (but continuous or dark line), because the objects were not purely transparent gases.