Final answer:
The component of the Milky Way Galaxy that accounts for interstellar extinction is the interstellar medium, which includes interstellar dust and gas that absorb and scatter light, thereby causing the dimming of distant stars. Unlike dark matter, which is detected through its gravitational effects, interstellar dust is visible through its obstruction and reddening of starlight.
Step-by-step explanation:
The phenomenon responsible for the dimming of light from distant objects in the Milky Way Galaxy is known as interstellar extinction. This effect is due to the interstellar medium (ISM), which consists of gas and dust that scatter and absorb starlight, thereby reducing its intensity by the time it reaches an observer. The interstellar dust can be identified when it obscures the light of stars located behind it, by the reddening and fainting of distant stars, or by infrared emissions which indicate the dust's heat radiation. The dust and gas that cause interstellar extinction are much more apparent in the plane of the Milky Way, and while they can block visible light effectively, other forms of light can sometimes penetrate this cosmic smog, aiding astronomers in mapping the structure of our galaxy.
Furthermore, it's important to note that interstellar extinction is different from the concept of dark matter, which constitutes a significant portion of the Galaxy's mass that is only detectable by its gravitational effects on visible matter. The existence of dark matter has been inferred from the way it influences the orbits of star clusters and dwarf galaxies.