Question

The density of interstellar dust is very low, yet it still blocks starlight because

A) the dust particles are irregular in shape.
B) it is so cold it absorbs higher energy photons.
C) there is 100 times more opaque gas than dust present in the ISM.
D) the dust particles are about the same size as the light waves they absorb.
E) ice particles reflect all light back toward their stars, not toward us.

Answer 1

Interstellar D) Dust blocks starlight as the particles are similar in size to the light waves they absorb, resulting in interstellar extinction and reddening.

Step-by-step explanation:

The density of interstellar dust is very low, yet it still blocks starlight primarily because D) the dust particles are about the same size as the light waves they absorb. These particles are efficient at blocking light, creating the phenomenon known as interstellar extinction and reddening. Interstellar dust particles consist of rocky cores with mantles made of ice and are about 10 to 100 nanometers in diameter, which corresponds to the wavelengths of visible light. This characteristic size makes them particularly effective at absorbing light, unlike interstellar gas, which is much more transparent and does not cause the observed reddening of starlight.