This image was taken on the night of 30th September/1st October 2011. It was taken with a Canon 200mm lens on a Canon 40D DSLR camera. It consists of 14 x10 min sub exposures at iso 800 (= total exposure time of 2hr 20min) that were stacked in Deep Sky Stacker and processed in Photoshop.

​

You can see more of Dave Smith's photographs on his website by going to our Links page.

​

What a wonderful picture! This magnificent emission nebula looks almost like the result of a moment of carelessness with a paint brush on the otherwise immaculate canvas of the night sky. The truth is far grander though. It’s actually a huge cloud of gas and dust glowing in the light of hydrogen alpha emission (656.3nm). The hydrogen component of the gas has been ionised, by vicious ultraviolet light, probably from the nearby star Menkhib (Xi Persei), which is a very hot spectral class O7 star with a surface temperature thought to be around 37,000 Kelvin. Menkhib is a member of the Perseus OB2 association and is the bright star just to the right of the nebula in Dave’s image.

​

As well as H-alpha, the nebula emits H-beta (486.1nm in the blue part of the visible spectrum), and also shows emissions due to oxygen and sulphur. In addition there is also considerable infra-red emission from the dust.

​

Sources differ with regard to estimates of the distance to the California Nebula, which range from around 1,000 light years to as much as 1,800 light years. Given its apparent dimension of 2.5 degrees in length (five times the diameter of the full Moon), these distances equate to a real length of from around 45 light years up to about 80 light years, whilst some sources quote it as being as much as 100 light years in length. Any of those makes it a huge structure. This is of course merely its size as projected onto the night sky. Its actual size will depend upon its orientation to our line of sight.

​

This brilliant daub of red painted upon the sky, which proclaims itself so brightly in photographs, belies the fact that it may be, in relative terms, little more than a fragment of gas and dust on the margin of a much larger complex of dark clouds of gas and dust, known as molecular clouds, that pervade this and many other parts of the sky within the Milky Way. These molecular clouds are the very stuff of new stars. Many of these dark nebulae were catalogued and photographed by the highly acclaimed nineteenth century American astronomer Edward Emerson Barnard (1857 to 1923), who it was that also discovered the California Nebula in about 1885. Barnard was an early pioneer of astro photography and in 1913 published his Photographic Atlas of Selected Regions of the Milky Way.