Tuesday, October 28, 2008

M45 - The Seven Sisters

This is a target I've been longing to bag for quite some time now. It's one of the most well known open clusters in the northern hemisphere, and an absolute beauty to behold in a pair of binoculars or wide field telescope. One thing you cannot see in this way though is the nebulosity that surrounds and envelopes the cluster - only a very large telescope or long exposure image will reveal the beauty of that.

Also know as Subaru in Japan (yes, the same as in the car, which
incidentally has only 6 stars on its logo), the Pleiades lies 440 light years away in Taurus, and is composed of over a thousand 100 million year old hot blue stars. These stars are shining upon a nearly (though unrelated) cloud of interstellar dust, which in turn then reflects the blue light back to us, and it is this that we see here as a faint nebulosity surrounding the stars.

With the clocks falling back an hour into GMT (where they should be in my book!) I took the opportunity to get out in the back garden to do some imaging. I was intending to have a go at the Great Andromeda Galaxy, but I saw the Pleiades rising above the hedge line and I could not resist! In hindsight I should have, as being only a shade over 30 degrees up in the mirk of Bristol (and more importantly the street light behind the hedge) I was never going to get the best out of my kit - the attenuation of light must have been pretty harsh to be honest. That aside, I'm somewhat pleased with the result - another keeper!

During processing I must have tried about half a dozen different curve manipulation paths on this one, with each run giving me a completely different result. I now firmly believe in working in the luminance channel separately from any colour channels even with one shot colour images as it helps enormously - after all it is the luminance that gives the details, not the colour. This is actually normal practice in CCD imaging, where you get the best, deepest, smoothest, and longest exposures for the luminance, then use 2x2 binning for the colour data.

In PixInsight this can easily be achieved on an already RGB image utilising the LAB colour space (ie, the luminance channel is processed separately from the 2 colour channels). In this case it allowed me to pull out the faint nebulosity without blowing the colours way out of proportion - especially the blues. In the end I settled for my own processed luminance image, and the colour data coming from an image off the Internet. The result is a tinted version of my captured data, and thus all of the details present were actually captured by my camera and only the hues "synthetic".

I'll settle for Andromeda another day .....


Anonymous Anonymous said...

Amazing shot Simon! I've tried the same but I don't that the field of view!

(Marcus E. from the BAS yahoo group).

9:12 pm  

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