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 .....

Scope & Camera Finally Meet!

On the night of the Lunar imaging that I posted previously, I also finally put my 20D on the end of my telescope at prime focus. I was happy I knew how the camera operated, and I had been playing with using my laptop to control the camera via a custom cable release controlled by the parallel port - which basically meant the laptop held the bulb down and did the exposure counting rather than me and my thumb :) I was ready for the next step in my imaging journey.

I needed something bright and easy to start with, so the first target was the Great Globular Cluster in Hercules - M13. It's one the brightest globular clusters in the Northern Hemisphere and is just visible to the naked eye on a good night. Although easily seem with 10x50 binoculars, the stars only really start to resolve out of the blob when you turn a telescope towards it. With hundreds of thousands of stars present, the more aperture you have to hand the more stars you can resolve. Visually, some people claim there are patterns inside the cluster - a propeller is quite often cited - though I do wonder if it's just a case of the classic "averted imagination" (which is our local societies take on the averted vision technique that some of the experienced observers tend to use when seeing things nobody else can!). I also have horrendous memories at university being made to count the number of stars in the cluster using a magnifying glass .... thank god for the invention of computers to do such tedious things for you! Anyway, on with the first image!


This image is a crop from a larger frame, and you can also see a small friend to the north east of the cluster called NGC 6207 - a 12th magnitude edge on galaxy. This is just a line of sight effect mind and the two are not related in any other way than their apparent position in the sky.

The image is a summation of 13 two and half minute exposures, stacked in Deep Sky Stacker, and given the obligatory PixInsight and Photoshop treatment. I'm finding now that I need to do around 3 attempts before I get one that I find satisfactory - and almost always the first one is never the best.

I felt I was on a roll by this time in the evenings preceedings. M13, a lunar mosaic, what more could I want .... Well, I really wanted to try to capture the North American Nebula, but knew my camera was not the most sensitive in the Hydrogen Alpha light that this nebula throws out in spades. This didn't stop me from wanting to have a go though! Unfortunately, I quickly realised that ther was no way I could spot the nebula in either the finder, 10x50's, or telescope itself (as mentioned in some of my previous posts) so I needed to have a leap of faith. I had a rough idea from a star chart I had to hand, but with only the finder to line up, it was a serious case of "point and hope"

Well, lady luck was obviously on my side again, as extremely faintly in the background of the image data was a nebula bursting to get out. It needed some heavy processing, but luckily it seemed to take it well, and this was the result.

I was a very happy man when I teased this data out of the set! It's a stack of 12 two and a half minute lights, and you can see quite a bit of detail in there when you start to look. Yes, a little noisy, but that's to be expected with the ISO, processing aggressiveness, and low frame count, but definitely a keeper :)

I performed the normal DSS stacking (with flats, darks, and bias frames), a hefty session in PixInsight, and a fair bit of tweaking, layering, and exposure balancing in Photoshop to get the best out of the data.

I'm rather proud of the result to be honest! The framing could not have been better (there's no cropping here). All in all the most successful imaging night to date! I suspect next time I won't be as lucky :(