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Rob Sellent

Observing Open Clusters

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Posted (edited)

Galaxies, Planets, Nebulae are pretty easy, I kind of know I'm observing one if I find one, but even with the star atlas in hand and knowing more or less the scope is pointing in the right direction, I'm not always sure I've found an Open Cluster :icon_scratch:. Sure, there are pretty easy ones to identify like the Double but for those more dispersed OCs, those in Cygnus or Cassiopeia for example, that all seem wrapped up with all the other stars when do you get that 'that's it' moment? To be honest, a lot of the time I'm just guessing so do you have any tricks or tips?

Thank you for you time and I hope this is in the right section :smile:

Edited by Rob Sellent
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They can be tricky blighters Rob, especially some of the smaller less distinct ones. This is where I find Skysafari so much better than any other paper atlas; by setting up the field of view circle to match your kit, setting the visible stellar magnitude to what you are seeing through the scope and finally setting the correct orientation, matching star patterns becomes very easy, and that makes pinning down the position of these objects much easier too. Identification is also made simple by actually matching the star pattern within the cluster.

Any use?

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6 minutes ago, Stu said:

Any use?

Just about everything you say Stu is of use! Seriously, your insight, knowledge, expertise, humility and kindness are an inspiration to everyone.

I think I'm going to have to get this Skysafari. It sounds a very useful tool to have in one's kit. I'm an old fashion fool and still use a beaten and worn paper atlas and considered myself something of a revolutionary when I got hold of interstellarum :smile:

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6 hours ago, Rob Sellent said:

I'm an old fashion fool and still use a beaten and worn paper atlas and considered myself something of a revolutionary when I got hold of interstellarum :smile:

In my heart I love paper atlases too Rob, and have many of them. The problem is, I just find the flexibility of apps like Skysafari so useful that I never use anything else when observing now. One simple thing is that they present as white stars on a black background, which my pea-sized brain finds much easier to interpret than having to compare a black on white image to the real thing! In general the view on Skysafari looks very similar to that through the scope when you've set it up correctly.

The one challenge is obviously managing the impact on your night vision, but with either careful control of brightness electronically or better still a good red film over the screen, I find it has no more impact than a red torch. Under a very dark sky this view would maybe change, if you are going for very challenging targets then probably best to memorize what you are looking for or revert to a paper atlas at the scope. For my general observing at home though the phone is the least of my dark adaptation worries with so much LP around.

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7 hours ago, Rob Sellent said:

Just about everything you say Stu is of use! Seriously, your insight, knowledge, expertise, humility and kindness are an inspiration to everyone.

 

I will ' second 'that

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I enjoy finding and observing open clusters. I often seem to stumble across them when panning around looking for something else. The challenge then is to work out which one you have come across !

When I started out with my old Tasco 60mm refractor, open clusters were one of the best DSO targets available to me so I spent quite a bit of time hunting them down with that little instrument and my parents old 8x30 birding binoculars.

I do have Sky Safari but I don't tend to use electronic devices out with me when observing so I relay on noting the relative position using my finders and use paper star charts to try and ID the target.

My favourite scope for open clusters is my Vixen 102mm F/6.5 refractor. Armed with a 40mm wide field 2 inch eyepiece I can see a 4 degree chunk of sky which is wonderful for not only picking up these star groupings but also seeing the context within which they sit.

One thing that adds to the fascination of open clusters for me is to find out when they were 1st noted. I get a little thrill thinking that I'm replicating the view that some of the great names in the history of astronomy saw many years ago. William Herschels name seems to come up a lot !

 

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I do have to say - most of the OC's I have observed seemed fairly obvious what they are - but having said that, I know I have really only gone after the "obvious" ones, and I have not really dug into any of the more 'open' (for lack of a better term) ones.

I can definitely see the SkySafari advice being of use - I do that all of the time when I am sitting on my couch - but rarely think of it at the EP!  I need to adjust my thinking some.

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13 minutes ago, KingNothing13 said:

I do have to say - most of the OC's I have observed seemed fairly obvious what they are - but having said that, I know I have really only gone after the "obvious" ones, and I have not really dug into any of the more 'open' (for lack of a better term) ones.

I can definitely see the SkySafari advice being of use - I do that all of the time when I am sitting on my couch - but rarely think of it at the EP!  I need to adjust my thinking some.

Many of them are actually quite small and easy to over look. Once you identify them you can push the mag up and often they become more distinct and easy to compare with the Skysafari image as the fainter stars become visible.

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Posted (edited)

@Stu with the general tendency towards lighting up gardens and streets with even more light, I have to agree that using a red-screened phone is the least of our worries. I've recently moved to a village with only about 300 inhabitants. You'd think we'd have reasonable skies but at night you could read in the steets. I'm having a 'battle' with the local council here with two street lights. Even the other neighbours aren't happy with them but the local officials just don't want to do anything. We've asked politely, we've written, we've sent photos etc and nothing. Anyway, rather than getting stressed or angered I've swotted up on a little trigonometry and have worked out how high I need a few wooden beams to erect some kind of sail-block. Come autumn, I'll get my DIY cap on and see what I can come up with.

@John not only a similar disposition towards finders but also towards low power surfing. It's that context I really like as well. When younger I used to be more inclined towards bigger aperture and higher power viewing but in my middling age I'm tending more towards less aperture, lower-power, wide field views. Obviously, this is not always suitable - skies can appear too washed out, and for planets and the Moon higher powers are 'better' but for low power the sky holds more than enough delights to keep one busy all night. Your Vixen 4" 6.5f must be a joy to use. It's a scope whose reputation is well documented and whose optics must be quite outstanding. On a similar note, I've recently put in an order for an old Vixen 4" 8.8f which might be even older than your own. I've been assured (by Markus at APM) that although the tube is scratched a little, its lens and collimation is still in excellent condition and working order. If everything goes alright, hopefully I'll have the OTA by August end and will try a little (unfair) shoot out with my TV76.

@KingNothing13 I agree that the Messier open clusters, for example, do seem pretty obvious, but sometimes - especially in these summer months - I stumble upon a tightish grouping of stars that could be an open cluster. The thing is I just don't know, so I was wondering if folk had any tips or tricks. I think the main thing to do judging from what John and Stu have said, is to note its position and use some kind of reference guide (Skysafari or a decent paper atlas) to see what was found.

Edited by Rob Sellent
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Congratulations on the forthcoming Vixen 102F Rob !

My Vixen is not a fluorite but an ED doublet from around 2000 / 2001. The Vixen you have ordered is the 1st generation Vixen 102mm fluorite (the 2nd gen were F/9) and could well be from as far back as the 1980's. I used to really lust for one of those but they were way out of my price range back then :rolleyes2:

The performance of the Vixen 102 flourites is, I understand, very, very, very close to that of the more recent Takahashi FC-100's which Stu and I and a few others are lucky enough to own.

Top of the performance tree as far as 4 inch refractors go I think :smiley:

 

 

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Many open clusters are determined as small and hazy, which become more resolved at high power. Perhaps jiggling the scope a little might assist to determine whether you are focused upon a cluster. Averted vision at high power assists to resolve some of fainter clusters into collective stars. Noting and checking your position, referencing a sky chart would ascertain to confirm which cluster you have located.

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Lovely scope Rob. As John says, I'm sure you won't be disappointed with those lovely fluorite views.

I have often lusted after John's 102 f6.5, but on the rare occasions that they have come up for sale I've not been in a position to buy. My widefield fixes are either with the FC100, or a lovely old Televue Genesis which I have; it's the third (and best) one I've owned and at 500mm focal length and a wonderful flat field, the views under a dark sky are very nice indeed. It is not an apo by any means, but at low to mid powers it is hard to beat.

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Wow, you guys have some very nice scopes. Taks, Televue, old-skool Vixens. For frac lovers, it doesn't get much better than that 🙂.  Seeing as its almost full Moon went out tonight to get a quick view of Saturn and Jupiter and thought I might be able to track down a cluster or two. Sadly after setting up clouds got in my way :BangHead:

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The important thing is to use a magnification, which should just about frame the entire open cluster.

 

So for the Pleiades you need very low magnifications <30x , whilst some tiny open clusters might require 100x magnifications.

If you can only see bits of a star cluster, then you will not recognise it for what it actually is.

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5 hours ago, darkskyastronomy said:

The important thing is to use a magnification, which should just about frame the entire open cluster.

 

So for the Pleiades you need very low magnifications <30x , whilst some tiny open clusters might require 100x magnifications.

If you can only see bits of a star cluster, then you will not recognise it for what it actually is.

To me, objects like the Pleiades look very nice when nicely framed by dark sky rather than just about filling the field of view, that way you can properly see the overall shape.

For some of the much smaller clusters, getting them to fill the fov is not really practical so it's a matter of finding an optimum magnification to show as many stars as possible to allow identification. Often they are still very small in the fov though.

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