The 21-cm line is one of the most important wavelengths in radio astronomy. It is produced mainly in
A) emission nebulae.
B) neutral hydrogen.
C) ionized hydrogen.
D) hot O and B stars.

Question

Quizplus · Accepted Answer

The 21-cm line is produced by neutral hydrogen atoms when the spins of the electron and proton flip from being parallel to antiparallel (or vice versa). This specific wavelength is crucial in radio astronomy for studying the structure and dynamics of galaxies, as neutral hydrogen is abundant in the interstellar medium.

The 21-Cm Line Is One of the Most Important Wavelengths