The California Nebula, an emission nebula in Perseus

The California Nebula, an emission nebula in Perseus

Image Credit & Copyright: J-P Metsavainio (

The California Nebula (NGC 1499) is a large emission nebula and star-forming cloud of around 100 light-years long, located some 1,000-1,500 light-years away in the Orion spiral arm of the Milky Way galaxy (where our Solar System is also located) in the constellation of Perseus, what makes it one of the nearest H II regions to Earth. It is so named because it appears to resemble the outline of the US State of California. It has a very low surface brightness and it’s very difficult to observe visually.

The California Nebula contains a hot blue-white star named Menkhib (also designated HD24912 and Xi Persei), by far the brightest star in this image. Menkhib is one of the hottest stars visible in the night sky; its surface temperature is about 37,000 Kelvin (about 66,000 degrees Fahrenheit, or more than six times hotter than the Sun). Because of its high temperature, it appears blue-white to the human eye. It has about 40 times the mass of the Sun and gives off 330,000 times the amount of light. Menkhib is a runaway star, and the fast stellar wind it blows is piling up in front of it to create a shock wave. This shock wave is heating up dust.

Menkhib, which is receding from us at about 20 kilometers per second, is part of an association of very hot stars that were born from the California nebula only a few million years ago. These massive and luminous stars are lighting up the nebula, as well as heating and ionizing it. In visible light, the ionized gas glows red, while in infrared light we see the heated dust.

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