The primary way that we observe the atomic hydrogen that makes up ...

[cnetterville]

The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with ________.
 
  A) radio telescopes observing at a wavelength of 21 centimeters
  B) X-ray telescopes
  C) space-based ultraviolet telescopes
  D) ground-based visible-light telescopes

Question 2

To calculate the masses of stars in a binary system, we must measure their ________.
 
  A) luminosities and distance from Earth B) orbital period and average orbital distance
  C) absolute magnitudes and luminosities D) spectral types and distance from Earth

[marict]

Answer to Question 1

A

Answer to Question 2

B

[cnetterville]

Thanks for the timely response, appreciate it

[bassamabas]

YES! Correct, THANKS for helping me on my review