Here's why:
* Emission Nebulae: These are clouds of gas and dust that are heated by nearby stars. The intense radiation from these stars causes the gas to become ionized, meaning its electrons are stripped away from their atoms. As the electrons recombine with the atoms, they release energy in the form of light, causing the nebula to glow.
Let's compare it to the other types:
* Reflection Nebulae: These nebulae reflect the light of nearby stars, similar to how a mirror reflects light. They don't emit their own light.
* Dark Nebulae: These nebulae are so dense that they block the light from stars behind them, appearing as dark patches against a brighter background.
In summary: Only emission nebulae are lit from within by the energized gas within the nebula itself.
