Estimate the ages of clusters 1 and 2. Significant credit will be given if you lay out how to solve the problem in words, even if you don't do the numerical calculations. By observing these stars over a long period of time, HST astronomers determine that Cepheid A has a pulsation period of 37 days, and Cepheid B has a pulsation period of 81 days. Again, explain how you know this without doing a calculation. Use the Cepheid data to compute the distances to Galaxy A and Galaxy B. Express your answers in megaparsecs.
Spectroscopic measurements are the key to determining galaxy redshifts, as discussed in class.
Explain in a few sentences what spectroscopy is, and what sort of instruments are required for carrying it out. In a schematic way, sketch the visible spectrum of a nearby galaxy. Assume the spectrum is characterized by absorption lines. Include a wavelength scale on the horizontal axis, but do not be concerned about the exact wavelengths of the spectral features.