29:62 GENERAL ASTRONOMY
Seventh Homework Set...Due April 09, 1999

1. For this problem you will have to root up some data from the lectures as well as in the textbook. Radio spectroscopy observations show us neutral hydrogen gas in the interstellar medium. Given the measured density of such hydrogen, how big a volume would be required to constitute 1 of material? What would be the mass of stars in such a volume? What does this tell you about the relative contribution to stars to gas in our galaxy?
2. The interatomic spacing for the sodium chloride molecule is 2.82 Angstroms (1 Angstrom = meters). Give the frequencies of the first three rotational transitions going from lowest frequency to highest.
3. The frequency of the rotational transition for Carbon Monoxide is 115 GHz. How cold would a molecular cloud have to be so that this line would not appear in emission?
4. Radio spectroscopy of molecular rotational transitions is done for two molecular clouds, creatively named Cloud A and Cloud B. In Cloud A the , , and transitions are of equal strength. In Cloud B the transition is bright, the transition is noticably weaker, and the transition is extremely weak. What can you say about a physical difference between these two clouds?
5. A cloud of neutral hydrogen is moving towards us at a speed of 70 kilometers per second. At what wavelength would one observe the radio spectral line characteristic of neutral hydrogen?

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