Final answer:
Starburst galaxies look ordinary in visible light due to interstellar dust obscuring their light, but appear extraordinary in infrared because the dust causes less obscuration at longer wavelengths, revealing their intense star-forming regions.
Step-by-step explanation:
Starburst galaxies might appear ordinary in visible light but extraordinary in infrared light because interstellar dust obscures their light less in the infrared spectrum. The infrared can penetrate dust and gas, revealing the intense stars being formed. Interstellar dust reddens and diminishes starlight in shorter wavelengths, making galaxies look less impressive in visible light. In contrast, interstellar extinction is much smaller at infrared wavelengths, allowing us to observe star formation and celestial structures that are otherwise hidden.
Since interstellar dust causes less obscuration at infrared wavelengths (e.g., 2 microns), we can see stars and galaxies that are more distant before their light is blocked. This is particularly useful for observing starburst galaxies, where a surge in star formation occurs, often following a galactic collision, making them much brighter and more detectable at large distances. This means that when observing in visible light, the light from distant stars is more likely to be absorbed and obscured by interstellar dust, making the galaxies appear ordinary. However, when observing in infrared light, which has longer wavelengths, the obscuration by interstellar dust is significantly reduced, allowing us to see stars that are more distant and usually hidden in the visible spectrum. This is why starburst galaxies appear extraordinary when observed in infrared light.