Globular star clusters close to the horizon plus the Eagle Nubula

Saturday 12th August 2017 10.30 to 11.30pm
Moon approaching last quarter and rose shortly after my observing session.
Observing with my f5 16 inch Dob.

I set my scope up in my Dad’s front garden this evening because it has a clear view to the south. The aim being to observe some new globular star clusters close to the horizon. To be honest, it was starting to get a bit boring observing the same stuff over and over again, and the only ways to observe new stuff are to go to a much darker site, go on holiday to Australia, or explore a lower patch of sky that’s previously been blocked by trees.

I soon discovered that nothing was visible in the finder scope this low down. The sky is lighter closer to the horizon and didn’t provide enough contrast. Instead, I used the Telrad to point the scope in roughly the right direction, then used my widest field eyepiece to scan for what I was looking for.

M22 proved reasonably easy to find, and reasonably impressive. It seemed to be quite spread out for a globular star cluster, lacking the usual concentrated core. It looked best in my Meade Super plossl, giving 80x magnification, rather than the 155x I normally use for globular clusters. I was denied a view of another globular cluster, M4, by a tree halfway down the street – which tells you how low it was.

I also managed to see M12 and M10 for the first time. (Also globular clusters.) They’d eluded me on previous occasions. Both were smaller and fainter, and needed 155x before I could see any individual stars.

A bonus was the Eagle Nebula. This looked best through an OIII filter at 60x. There are three bright stars at one end, and a cluster of about a dozen stars at the other end, with some cloudiness in-between. A UHC filter showed the nebulosity as well, but it wasn’t so pronounced. Without a filter, the cloudiness wasn’t visible at all. The fact that the Eagle Nebula is located by some prominent stars is handy, which should make it easy to point out to beginners. I can well imagine this nebula is a main attraction in more southern countries where it’s higher in the sky. If it’s clearly visible this low down it must be really impressive elsewhere.

I also showed my girlfriend Saturn, which she’d never seen before. It wasn’t a bad view for how low it was.  So there we are. It’s not every night I can say I’ve seen four new objects. Plus I saw the brightest meteor I’ve ever seen. If you want to see these globular clusters for yourself, and the Eagle Nebula, now is the right time of year.

David Geary

2 Responses

  1. Well done for spotting the Eagle visually! Satisfying isn’t it?! I bought a 12″ dob for doing this sort of thing, but found it little help, as the problem was contrast and not light grasp from my garden. So I sold it and now use electronic assistance in the form of the PD camera and my 8″ SCT – that’s what I used for the images for the Eagle I posted.

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