The extinction of starlight due to the interstellar medium
I. is the greatest in the ultraviolet.
II. is the greatest in the infrared.
III. is caused by ionized hydrogen.
IV. is caused by dust particles.
A) I,III
B) II III
C) I, IV
D) II IV
E) only IV

Question

Quizplus · Accepted Answer

The extinction of starlight due to the interstellar medium is caused by dust particles, which absorb and scatter the starlight, leading to a decrease in intensity. This extinction is the greatest in the ultraviolet (UV) and has a significant effect in the blue and visible parts of the spectrum. Therefore, choices I and II are not correct. While the interstellar medium does contain ionized hydrogen, this is not the cause of extinction. Therefore, choice III is not correct. Dust particles are the primary cause of extinction, hence choice IV is correct. Therefore, the correct answer is C) I, IV. The extinction of starlight due to the interstellar medium is caused by dust particles, which scatter and absorb light. Therefore, choice IV is correct. While both ultraviolet and infrared light can be affected by dust extinction, the extinction is actually greater in the visible and near-infrared wavelengths (not mentioned as an option). Ionized hydrogen can also affect some wavelengths of light, but it is not the primary cause of extinction, making choices I and III incorrect. Therefore, the best choice is C, which includes the correct answer of IV only.

The Extinction of Starlight Due to the Interstellar Medium