Why is Newton's version of Kepler's third law so useful to ...

[abc]

Why is Newton's version of Kepler's third law so useful to astronomers?
 
  A) It allows us to calculate distances to distant objects.
  B) It can be used to determine the masses of many distant objects.
  C) It tells us that more-distant planets orbit the Sun more slowly.
  D) It explains why objects spin faster when they shrink in size.

Question 2

Stellar parallax is the apparent
 
  A) shift in position of nearby stars as the Earth moves around the Sun
  B) westward motion of a planet with respect to the background stars
  C) shift in position of nearby stars as the Sun moves about the center of the galaxy
  D) shift in position of nearby stars as the Earth rotates on its axis

[Brummell1998]

Answer to Question 1

B

Answer to Question 2

A

[abc]

Thanks for the timely response, appreciate it

[scottmt]

Gracias!