29:62 GENERAL ASTRONOMY
Eighth Homework Set...Due April 14, 1999

1. A certain type of star is distributed with height above the galactic plane in a way which is describable by a scale height parsecs. What fraction of such stars are more than 700 parsecs above the plane?
2. A distant nebula has a ring-like appearance. Spectroscopic observations are made of a line which has a rest wavelength of 500.00 nanometers. A spectrum is taken of light from the very center of the nebula. The spectrum shows this spectral line split into two lines, one which has an observed wavelength of 499.84 nm and the other a wavelength of 500.17 nm.

   A spectrum taken at the edge of the nebula shows a single spectral line, with a wavelength of 500.00 nm. The radius of the ring is 180.0 arcseconds. Ten years later, another image is taken, and the radius is measured to be 182.0 arcseconds. How far away is the nebula? Your discussion should describe the physical significance of the data given above. : It might help to draw a diagram incorporating the above data before getting started

3. How bright would Betelgeuse be (i.e. what would its apparent magnitude be) if it were at the galactic center? For the purposes of this problem, ignore interstellar extinction, as would be the case, for instance, if it were high above the galactic plane.
4. Using numbers supplied in lecture or in the book, calculate the gas pressure in (a) the neutral hydrogen in the interstellar medium (b) molecular clouds. Compare this with the gas pressure on the surface of the Earth.
5. You are home, engrossed in reading your astronomy book about the Hubble Deep Field. As is typical for Iowa in Springtime, a severe thunderstorm develops and knocks out the electric power. You can't stand the idea of being interrupted! You recall that you have a bowling ball in your apartment and that rotating objects possess rotational kinetic energy. Your bowling ball has a mass of 5 kilograms and a radius of 10 centimeters. You speed it up so that it rotates on its axis 100 times per second, and (somehow) channel its energy to your electric light. What slowdown rate do you need to supply sufficient power to your 75 Watt lamp? How long can you continue to read with the bowling ball as your energy source?

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