The spiral-arm structure of the Milky Way Galaxy has been measured and evaluated MOST effectively by observations of
A) globular clusters in the halo of the Galaxy.
B) Balmer emission lines of visible radiation from hydrogen.
C) 21-cm radiation from interstellar hydrogen and the distribution of young stars.
D) Lyman UV radiation from hot hydrogen gas.

Question

Quizplus · Accepted Answer

The spiral-arm structure of the Milky Way Galaxy has been most effectively mapped through observations of 21-cm radiation from interstellar hydrogen and the distribution of young stars. This is because 21-cm radiation, which is a form of radio waves, can penetrate the dense dust clouds in the galaxy, allowing astronomers to map the structure of the galaxy, including its spiral arms, with greater accuracy. Additionally, the distribution of young stars, which tend to form in the spiral arms, helps in tracing the shape and location of these arms.

The Spiral-Arm Structure of the Milky Way Galaxy Has Been