An HII region is a large cloud of gas that is primarily made up of hydrogen atoms that have been ionized by ultraviolet radiation from nearby young stars. The "HII" (pronounced "H-two") refers to hydrogen that has lost its electron, becoming a positively charged ion. These regions are often found around hot, young stars and are characterized by their glowing appearance due to the recombination of electrons with hydrogen ions, emitting light primarily in the red part of the spectrum. HII regions are often associated with star formation.
- A type of emission nebula where the ionized hydrogen is the dominant component.
- They are often associated with regions of active star formation.
- Rosette Nebula: An HII region known for its large, circular structure and active star formation.
- Luminous Nebulae: Regions like the Tarantula Nebula in the Large Magellanic Cloud.
