Astronomy Homework College level

Need these short essay questions done ASAP.  Valid reputable sources are needed as is a works cited.   Interned sources are fine, but no wiki or yahoo answers etc.  Anywhere from a couple paragraphs or a page is fine for length, maybe 2-3 pages times new roman 12 point double spaced total if needed.

1

How does the use of H II regions to find a galaxy's distance differ from the use of Cepheid variables? in question 4 concentrate on the places we find H II regions and Cepheid variables and the distances that each can be observed. How bright are each? Are there any differences in accuracy? How do we know? How is their brightness used to determine distance?

2

How does the cluster method tell us the mass of galaxies?  Question 2 requires quite a few assumptions (what are they?). Be sure to consider gravitation and redshift as you research your response.

3

What evidence do we have that the center of our galaxy is a powerful source of energy?  Here’s a hint for question 5 – Sagittarius A. What do we know about it? What can we assume from this information? What evidence supports those assumptions and observations?