How did Harlow Shapley use the period-luminosity relationship of ...

[luminitza]

How did Harlow Shapley use the period-luminosity relationship of RR Lyrae variables to determine the size of the Milky Way galaxy?
 
  a. He determined the proper motion of globular clusters in the outer disk of the galaxy.
  b. He found the distances to individual variables free floating in the halo.
  c. He found the distances to open clusters found throughout the disk of the galaxy.
  d. He found the distances to globular clusters distributed about the center of the galaxy.

Question 2

What causes the outward gas pressure that balances the inward pull of gravity in a main-sequence star?
 
  a. the rapid outward flow of gas
  b. the rapid inward flow of the gas
  c. the high temperature of the gas
  d. the high density of the gas
  e. the high temperature and the high density of the gas

[aruss1303]

Answer to Question 1

d

Answer to Question 2

e

[luminitza]

Thank you!

[aruss1303]

Always glad to help...