Which of these colors of light passes most easily through interstellar clouds? (a) red light (b) green light (c) blue light
Interstellar Dust. Describe how our view of the night sky would be different if there were no dust grains in the interstellar medium.
The Correct Answer and Explanation is:
Correct Answer:
(a) red light
Explanation
Interstellar clouds, often called nebulae, contain gas and interstellar dust grains—tiny solid particles made of elements like carbon, silicon, and oxygen. These dust grains scatter and absorb light, a process known as interstellar extinction. However, not all colors of light are affected equally.
Shorter wavelengths (like blue light) are scattered more effectively than longer wavelengths (like red light). This is similar to why Earth’s sky appears blue—molecules in Earth’s atmosphere scatter blue light more than red. In space, blue and green light are scattered and absorbed more, making them less able to pass through dust clouds. In contrast, red light, which has a longer wavelength, is less affected by dust and thus passes more easily through interstellar clouds.
This scattering causes a phenomenon called interstellar reddening—stars viewed through dust appear redder than they truly are, because the blue light has been scattered away.
What If There Were No Interstellar Dust?
If there were no dust grains in the interstellar medium:
- The night sky would appear clearer and more colorful. Light from stars and distant galaxies would travel to us without being scattered or absorbed. This would dramatically increase our ability to see fainter and more distant objects.
- We would observe more ultraviolet and blue light from stars. Currently, dust filters out much of this shorter-wavelength light. Without dust, we would see the true colors and brightness of stars more accurately.
- The Milky Way’s dark dust lanes—those dark, obscured regions cutting through the galactic plane—would vanish, revealing a more uniformly bright and detailed view of the galaxy.
- Star formation regions, currently hidden inside dusty molecular clouds, would be fully visible in optical light rather than only in infrared or radio.
In summary, red light passes most easily through interstellar clouds due to its longer wavelength, and without interstellar dust, our view of the cosmos would be far clearer and more complete in visible light.
