M27 - as imaged by me on 14 August 2010
M27 – the Dumbell Nebula – is in the small and inconspicuous constellation of Vulpecula (the little fox), fairly high in the sky in the summer. It is a planetary nebula. The star at its centre cast off most of its gas about 48,000 years ago, which has now expanded to be a shell about 1.2 light years across, still expanding at between 9 and 20 miles a second.
I only saw this for the first time about a week ago, observed visually, looking like a blob of grey fuzziness floating in front of a rich field of stars. My first attempt at imaging it caught lots of (inaccurate) colour, but was very disappointing. I had to try again.
This was taken with an Atik 16ic specialist CCD camera attached to my Celestron CPC800 telescope. With the help of a “focal reducer” the telescope is the equivalent of a 1260mm lens at f6.3. The telescope tracks the stars, but is in alt-azimuth mode so the view seems to rotate as the earth turns. This meant that I can only realistically take 30 second exposures without the objects blurring because of movement. I took about 20 of these and combined them using software. (Maxim DL) This gives the effect of taking a much longer exposure and allows you to “average out” random noise. Astrophotography is the lowest of low-light photography and images are always noisy – there is almost as much “random stuff” happening on the chip as there are photons hitting it. As part of this processing, I took “dark” frames – images only showing what the chip is capturing without light – so you can subtract it leaving the light itself, which is what you want.
I am very pleased with this image. You can see the central star (magnitude 13.8) very clearly and if you look closely its companion is visible just below it – magnitude 17 (very dim indeed). Some photos show more detail in the gas clouds and more of the gas, but this one is a “keeper”.
