Stories from Physics for 11-14 14-16
Nebulae are known for their bright colours, an effect that can occur through different processes.
- Emission nebulae consist of a cloud of ionised gas containing or close to some very bright stars emitting ultraviolet (UV) radiation. The UV radiation is absorbed by the gas and leads to the excitement of electrons, which in turn leads to the emission of visible light. Most emission nebulae appear deep red due to emission at the hydrogen α-line at 656 nm.
- Reflection nebulae are visible as they reflect light from other stars. Reflection nebulae appear blue due to the same kind of scattering of light that makes the sky appear blue.