Final answer:
Radio waves of 21-cm wavelength pass through interstellar dust without being blocked or absorbed, allowing astronomers to detect hydrogen atoms throughout the galaxy. Infrared and radio radiation also flow unimpeded past interstellar dust particles, reaching telescopes with hardly any dimming.
Step-by-step explanation:
The Milky Way doesn't have enormous radio waves because radio waves of 21-cm wavelength pass through interstellar dust without being blocked or absorbed. This enables astronomers to detect hydrogen atoms throughout the galaxy. Infrared and radio radiation, which have long wavelengths compared to the sizes of interstellar dust grains, flow unimpeded past the dust particles and reach telescopes with hardly any dimming. Therefore, radio waves in the Milky Way are not blocked or absorbed by interstellar dust, allowing them to be detected.