H I clouds can be observed using _____.
A) optical telescopes above the earth's atmosphere
B) 21-cm radiation
C) x-ray radiation
D) infrared radiation
E) ultraviolet radiation

Question

Quizplus · Accepted Answer

H I (neutral hydrogen) clouds are primarily observed using the 21-cm radiation line. This specific wavelength corresponds to the hyperfine transition of neutral hydrogen and is a fundamental tool in radio astronomy for studying the interstellar medium.

H I Clouds Can Be Observed Using _____