This is a nebula that I have previously imaged using a DSLR camera. In fact, it was the first object I photographed with the 72ED refractor. It was in a good position in the sky when the clouds cleared for a few days in mid January, so I decided to give it another go with my astrocamera.

The California Nebula is also known as Sh2-220, or NGC1499 and its Wikipedia page has some more information about it. It is an emission nebula in the constellation Perseus. It is around 1000 light years from Earth, and its light emission is the result of fluorescence of the gases in the nebula caused by the radiant energy of the star Menkib (or ξ Persei), seen near the bottom of the image slightly to the right of centre.

The colour mapping for this image is a version of the Hubble Palette, where the emitted light from the different gases in the nebula are mapped as Sulphur to red, Hydrogen to green, and Oxygen to blue. I have adjusted the colours generated by such mapping to try to give a more pleasing image, because intially the dominant colour is green due to the much stronger signal from this gas than from any others found in space. After balancing the colours, I then used the Hydrogen only image as a luminance layer to define the brightness of the image. Stars were added from the red, green and blue filters which captured much shorter exposures in an effort to represent something close to the true colours of the stars.

You can view this image in the WorldWideTelescope by clicking here.