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