NGC1499 - the California Nebula is a HII emission nebula in the constellation of Perseus.
Named after the US State, due to it's shape resembling the state's boundaries, the nebula is approx. 1,000 light years away and can be seen due to the excitation of the cloud by the O7 star Menkib (ξ Per). Menkib is the bright star seen in the bottom middle of the image, below the nebula. It is one of the hottest stars in our galaxy with a surface temperature of about 35,000°C and is about 250,000 × brighter than our Sun. It's diameter is also 14 × that of the Sun and it's known to be a runaway star, which would have been formed in a Giant Molecular Cloud & then ejected either by a supernova, or gravitational fling by a close neighbour. It's by pure chance that it is in the position to illuminate this HII region at this current time.
For more info. see the Wikipedia entry.