Hi, I was wondering if somebody could help me to answer any of the following questions about galaxies. 1. Describe the major types of Galaxies, including information about their gas content, morphology and evidence for current star formation. 2. What are the similarities and differences between spiral and elliptical galaxies and what causes their different shapes. 3. Why do random encounters play a much greater role in the evolution of galaxies than they do for stars? 4. How do astronomers find the masses of galaxies? (include the parameters they measure).