Messier 2

[PhotoGav]

It has been ages since I last posted a deep sky image. I suppose the summer and weather are to blame. Anyway, finally I have something to share with you all. I didn't think I would as this target is low down over neighbours' roofs from my back garden and as the subs came in, I was expecting a far worse result. This is just about good enough to not confine to the bin! It has taken a long time to gather the data, thanks to the incessant rain and cloud. Seizing the occassional capture opportunities was far easier thanks to having the observatory. Everyone always said an obsy is the best upgrade and now, one and a half years on, I am inclined to completely agree! Anyway, I digress...

Messier 2 is an elliptical globular cluster about 37,000 light years away in the constellation of Aquarius. It is one of the largest globular clusters known in the Milky Way, though the number of stars it contains, around 150,000, is relatively low for a globular. Consequently its average density is low for a glob at around 0.04 solar masses per cubic light year. It was first discovered on September 11th 1746 by Maraldi, but he didn't catalogue it. Fourteen years later to the day, September 11th 1760, Messier discovered it and added it to his catalogue. No doubt annoyed to have not found a comet, yet again!

Technical data:
LRGB = 12 x 600s each
TOTAL = 8 hours

Celestron EdgeHD 800, QSI 683-WSG8, HEQ5 Pro, Baader 1.25" filters.

As I mentioned earlier, this is better than I had expected, but I am not convinced by the star shapes. Not sure if this is down to poor guiding through the low atmosphere or poor collimation. Further tests will reveal the answer to that one. I had also intended to gather more data for this project as the image is a bit noisy, but the Sky Gods and time decided that wouldn't be possible this year. Oh well, at least I finally have something to share with the world!

Clear skies all!

[domstar]

What a beauty. My favourite glob- I wish I could see it like that. Great write-up too.

[cfpendock]

Very nice stars colours, Gav.  And congratulations on having found some clear sky!  But I see what what you mean about the star shapes, something not quite right.

Chris

[toxic]

great image and star control 

[PhotoGav]

Thank you for your kind comments Chris, Chris and Domstar.

I had a look at collimation and polar alignment this evening while waiting for the Moon to wend its way towards the horizon. Collimation looks fine:

However, my polar alignment was not great, PHD2 Guiding Assistant was reporting a PA Error of 5 arc min. I was hoping to use the new Static Polar Alignment tool in PHD2 to get better alignment, but my QSI wouldn't play ball (fair enough, it's not really a guidecam after all!!) so I couldn't try that. Instead I used Alignmaster as usual and improved my PA. PHD2 Guiding Assistant reported a PA Error of 0.3 arc min after the re-alignment. I'm much happier with that!

So, I'm inclined to think that the dodgy star shapes are a result of poor guiding through the thick low level atmosphere. It will be interesting to see how my current project, NGC 891, turns out. Fingers crossed!

[Barry-Wilson]

I really like the control on the star colouring, you have balance between the yellows and blues and have resisted the temptation to over saturate.  Great image Gav.

I'm sure your PA accuracy has had an effect on tightness and star shape - a technical and disciplined approach to capture and its mechanics pays dividends, even if each is a marginal gain in quality.

[PhotoGav]

Thank you Barry (long time no speak - I hope all is well!). Yes, methodical and accurate is the required approach to data capture. I now have enough data to do a quick process on my current project, so it will be interesting to see what the stars look like. Guiding last night was much improved following the PA tweaks. It was such a joy to have a reasonably clear night last night and do some proper data gathering at last! Hopefully tomorrow night will be clear and crisp too, so once the Moon has set it will be all systems go!

[Piero]

Great image and a great target! I always enjoy spending some time observing M15 and M2 when visible.

Thanks for sharing.