Extragalactic Astronomy -
Fall 2012
Homework #1 - due August 22
1. What are the four components of the Milky Way?
2. What fraction of the mass of the Milky Way is dark matter?
3. Find the wavelength (in microns) of the peak of a blackbody spectrum
for an object with a surface temperature of 20,000 K. Convert
this wavelength into a frequency (in Hz) and an energy (in eV).
4. Draw a Hertzsprung-Russell diagram with axes of luminosity in solar
units and temperature. Indicate the positions of the main
sequence, giant stars, and white dwarfs. Indicate the positions
of stars of 0.2, 1, and 10 solar masses along the main sequence.
5. Starting from the Hubble expansion law, v = H0 D, find the age of the universe
under the assumption that there has been no acceleration or
deceleration over the lifetime of the
universe. Use H0 = 71 (km/s)/Mpc and explain your
reasoning as to why the specific form of the Hubble expansion law
implies that the universe
has a finite age.
6. Determine how the dynamical time scale for a gravitationally bound
system with fixed density
scales with the radius of the system R.
7. List three pieces of evidence for the Big Bang.
8. In what ranges of wavelengths is it possible to make observations of
astronomical objects from the ground?
9. What are IRAS galaxies?
10. What is the angular resolution of the Chandra X-ray observatory and
how does it compare to that of ground-based optical observatories?