|Right ascension||04h 03m 18s|
|Declination||+36° 25′ 18″|
|Type of object||Diffuse nebula|
|Dimensions||10° × 1.5°|
|Distance from Earth||1,467±75 ly|
The California nebula (NGC 1499) is a diffuse nebula in the constellation of Perseus and not far from the Pleiades. Named for its resemblance to the state of California, the nebula is found the Orion Arm of the Milky Way, the same arm as Earth and the Sun are situated in. The nebula is illuminated by the radiation generated by the star Xi Persei (ξ Persei). The nebula is a fairly popular target for astrophotography.
Properties and Structure
The California nebula is located approximately 1,500 light years from Earth and can be observed to have an apparent length of around 10° and width of 1.5°. This gives it a physical size of around 260 by 39 light years. The nebula is thought to have a mass of around 1.12×105 solar masses, making it the largest giant molecular cloud within 500 parsecs (1,630 light years) of the Sun. This means it is similar is size and mass to the famous Orion nebula. There are known to be many dark nebulae in this are. These consist of dark gas and dust that obscure background light and so it is likely that the California nebula is simply the brightest are of a large nebula that is visible, with the rest being obscured by intervening gas and dust.
The nebula's red glowing appearance is due to the star Xi Persei (ξ Persei). As an O type star, it emits large quantities of radiation in the ultraviolet portion of the electromagnetic spectrum. This ionizes hydrogen gas present within the nebula creating free protons and electrons. When a proton and an electron recombine to form a hydrogen atom, they emit a characteristic red light that can be seen from images of the nebula.