How does gravitational lensing tell us about the mass of a galaxy ...

[jon_i]

How does gravitational lensing tell us about the mass of a galaxy cluster?
 
  A) The lensing broadens spectral lines, and we can use the broadening to weigh the cluster.
  B) Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.
  C) The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law.
  D) Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster.

Question 2

What are the standard units for luminosity?
 
  A) Watts
  B) Newtons
  C) Joules
  D) kilograms
  E) Watts per second

[Jayson]

Answer to Question 1

B

Answer to Question 2

A

[jon_i]

Great answer, keep it coming

[mcarey591]

Thanks for the timely response, appreciate it