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Is it the conditions or my scope?


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I'm new to the hobby and after doing a fair amount of searching about with my binoculars and familiarizing myself with the constellations I decided to purchase my first scope. Based on reviews and opinions I had read I ordered a Orion XT6 Dobsonian. I live about five miles outsidein a large metropolitan area so the sky is not as dark as I would like. We have only had about three or four clear nights in the past month to use the new scope. So far I have observed Saturn, M13, and some doubles. For EPs I have a 40mm, 25mm, 10mm, 5mm, 2x Barlow and a variable zoom 24 - 8mm. The question I have is that on the nights I was able to use the scope M13, although easily identifiable, does not appear much more resolved than a smudge. Could this just the limitations of the equipment or is it likely the result of light pollution and / or viewing conditions? The scope has been properly collimated. I have read enough to have realistic expectations of what I can and cannot see, but I still don't have the practical knowledge to determine what the limitations of my scope are or whether or not I am up against poor seeing conditions. I thought I would ask you all for your input. Thanks!

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Hi Treewick,

It's most likely that it's a mixture of both. The light pollution you experience won't help your cause in brightening the objects you see (M13), however, with globular clusters, aperture definately rules. I have a 4.75" refractor, and to me M13 seems no more than a smudge, but that's not the point. What you're looking at is a group of over 1 million stars, held together by gravity, just outside the Milky Way. It's truly fascinating. We all crave great views, which can be achieved with scopes like 12" Dobs (Just an example), however the views aren't everything.

Coming to understand the limitations of your telescope is all part of becoming a better amateur astronomer. Finding objects that look great in your telescope is a brilliant feeling. Some objects naturally require more aperture than others, it's just finding out what to look at.

Sorry for blabbering :)

Clear Skies!

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Hi

With a 6" scope M13 should be slightly mottled in apearence with some outer stars resolved.

However light pollution will deteriorate this view quite considerably if you are near a big city.

Try if you can to observe it from a dark sky sight, it will improve the view immensely.

Regards Steve

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Thanks for the reply. I was thrilled to see what I saw! not disappointed in the least, just trying to understand where the limitations were. On the third night I was able to tease out a little more clarity with averted viewing. I cant wait to get to a dark sight on a clear night with the scope though.

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I'm not a fan of very high powers (prefer smaller & sharper to bigger & fuzzier)

but M13, and globular clusters in general, look better at a higher mag, 100 - 200x.

At low power they just don't look nearly as good. A bit of haze kills 'em too.

Another factor at this time of year is that it takes ages to get dark, so the temptation

is to observe when it's still too light to bring out the detail in DSOs.

Regards, Ed.

Edited by NGC 1502
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Viewing globular clusters at high magnification (150x and higher) makes light pollution almost irrelevant. It is possible to resolve the stars in M13 with a 102mm scope, in my experience anyway. M3 is also possible on very clear nights, usually with averted vision. I have glimpsed the stars in M3 fron an urban location with a small scope. A 150mm scope should perform much better, if the eyepieces are up to it and the tracking is not too problematic (I don't know if the dob is undriven).

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The scope does not have any tracking mechanisms, it's just manually operated.. The eyepieces are all Orion Plossl, the 40mm is a Orion Highlight series Plossl. The higher magnification EP that I have is an Orion Stratus but I have not been using that or the zoom EP (Celestron) to try and view this cluster because of the blurring at magnification. So far the best viewing I have been able to obtain has been with the 25mm.

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Viewing globular clusters at high magnification (150x and higher) makes light pollution almost irrelevant.

Have to disagree with ya there. Light Pollution does not disappear at higher power, or all city dwellers would simply observe at 150x and higher and be able to make out the North American Nebula.:)

Globular clusters benefit like nearly all DSO, from dark skies.

Regards Steve

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Higher powers attenuate nebulae, so magnification is not a general solution. And it only applies to small scopes. With my small scope, at high magnification, I can achieve a dark background and similar views to those from a darker site, for small stellar targets that are not attenuated by the magnification. With a larger scope, the same magnification would of course still yield a milky background.

For example, swamp thing, if you took your 10" dob to my back yard, you would need to use 375x magnification to get the background darkness I get at 150x.

But I do agree that dark skies make an enormous difference. I'm only making the point that some enjoyable and successful viewing is possible from light polluted locations - important for those of us that can't get away so easily to dark sites.

Edited by Ags
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