Open clusters: Never really sure what I'm looking for.

[cantab]

So I've looked for a few open clusters with my binoculars, but a lot of the time, I'm not really sure what I should be looking for, and whether I've seen it or not. The big obvious ones like the Pleiades, Hyades, and Alpha Persei Association are easily apparent, but then when I've looked for things like the Perseus Double Cluster, M34 in Perseus, or M35 in Gemini, I'm just seeing starfields, with nothing that stands out as distinct.

Stellarium seems to "back this up", the clusters don't exactly jump out in an FOV matching my bins and with the light pollution turned up to 8 (which about matches my site I think).

Any pointers on how to know when I'm looking at these things? (Preferably not sketching! I had to sketch in geology fieldwork and labwork, and I was rubbish at it and disliked it.)

[Capricorn]

None of them exactly stand out, well almost none.

The double cluster is I see an NGC number not a Messier and these are, tend to be, dimmer. Otherwise Messier would have logged them. Also the milky way is in the same are.

They can be seen in binoculars, I use 8x42's to look round and they are visible. I find it best to use Cassiopeia to point at them.

They appear as 2 small grey patches, which if you look for a while slowly display themselves as a sort of cloud of dim stars. No more. Also the measure of Magnitude is misleading as the magnitude is the sum of all the light off of the cluster. If the cluster is spread out, it's a cluster so it has to be, then the brightness of a portion of it is much reduced.

The ones in Hercules are much the same.

You would find that darker skies help, and what binoculars have you? Magnification is not good on very dim objects.

[cantab]

Bresser 10x50s. Nothing high-end but I think they give OK views. (At least until the objectives fog up!)

[magic612]

One thing that may help you is understanding the different sizes of various clusters. A program like Cartes du Ciel (also free) or checking the apparent size on Wikipedia entries will let you know the approximate size of clusters, then you can estimate whether it is something you may be able to spot in binoculars, or whether a telescope is required.

For example, I know what the Double Cluster looks like in binoculars (7x50's) and it's not much - more like a hazy patch that I "know" is those two clusters, but no real detail is evident. Why? Well, Cartes du Ciel lists both clusters at about 18 arc minutes across. 18 arc minutes is less than 1/3 of a degree (there are 60 arc minutes in one degree). So if you are looking with binoculars that give you a 7 degree field of view (7 x 60 = 420 arc minutes) like many 7x50's will, 18 arc minutes only takes up 4% of the width of the field of view. So that will look rather small in binoculars, and that's really when a telescope is needed.

And in a one degree field of view of low-power eyepieces of most telescopes, those two clusters at 18 arc minutes across right next to each other will now take up nearly the entire field of view! It's a big difference - and a 1.5 degree field of view with very long f/l eyepieces looks much better, I think.

Another example is looking at some clusters in Cassiopeia - NGC457 (the "E.T." or "Owl" cluster) is something I can spot in binoculars because I know it is there, but not see the "eyes" or the rest of the cluster either. Again, similar size, at 20 arc minutes, but not something that is going to jump out at you compared to, say, the Pleiades that are 110 arc minutes across (nearly 2 full degrees!) and actually difficult to frame in most telescopes.

Open clusters are of varying sizes, and distances from Earth. This will affect what you see, and what magnification is required to see each. Knowing the size of clusters beforehand will give you a sense of what magnification will be needed to spot, and identify, them more easily.

Hope that helps!

[rory]

remember open clusters as i understand it are lightly bound togeather by gravity and are moving apart . so some open clusters litterally look like stars that are somewhat closer togeather than normal field stars,and many can look bland in some cases. others look alot more obvious.

i think also (like me) novices/ beginers tend not to see them in the same light as it were compared to experienced astronomers.

saying that ,m44 (beehive) is stunning in my opinion.

i might be talking **** but thats my understanding cantab.

clear skies mate...

[cantab]

Hmm, so basically it's a case of they're smaller than I think. I guess experience will teach me how big stuff is.

Of course the Moon's only half a degree across, but it seems to end up subjectively looking bigger.

[GJBC]

The double cluster is I see an NGC number not a Messier and these are, tend to be, dimmer. Otherwise Messier would have logged them.

I can see where Capricorn is coming from but these would have been quite visible to Messier with the naked eye and too wide spread for him to log them. very much like the great orion nebular as it is known they knew it was there and not a comet.

for the newbies a little bit about the messier catalouge:

messier began recording the position of objects he and his assistant found as they were systematically scanning the sky for the returning Halley's comet in 1758 or early 1759. he then knew he had seen the object before and could discount spending time observing the. in his words "time wasting objects to avoid"

an example would be M13 might have looked like a comet through an older telescope being used then, they would not have resolved the object as well as we can these days. but by taking note of it location he was able to go back there on subsequent evenings over a period of time to see if it had moved. if it had it was possibly a comet and then he would try and track it down again if it did not move it was logged this was his thirteenth objecto to avoid on the list

messier located the comet on 27 Jan 1759 but his boss would not let him announce the discovery it was not to mater though, the comet had been re discovered on Christmas day 1758 by a German farmer and amateur astronomer named Johann Georg Palitzc.

could messier had found it earlier? it does beg that question. messiers chart had been incorrectly prepared by Nicholas De l’isle Astronomer to the French Navy Messier's "Boss"

Messier first list was only 45 items and published in 1771 not all the objects were discovered by Messier and With the help of the mathematician Pierre Méchain, the list grew to 68 objects in 1780 . and that grew later to 103 in 1781 and that is where it stayed until the 20th century with M110 being the final addition in 1967 out of the 103 on the messier list messier only discovered 40, 27 were discovered by Méchain with the remainder being supplied by other astronomers to assist in making the list.

Messier never knew that in the beginning of march (ish) you can see all the object he had listed this was not done until Gerry Rattley of Dugas, Arizona completed it on the night of March 23/24, 1985.

So there that has taken all night to put together and sorry for whittleing on for so long if you have read it all thanks. now you can have a beer.

[Double Kick Drum]

I used to have similar problems when I had a pair of 10x50s and never used to really appreciate open clusters much except for the show stoppers (Pleiades, Beehive etc)

Another brightish cluster worth trying is M39 in Cygnus which I think is a bit bigger and more impressive than M34 and M35.

Alternatively, I think M37 in Auriga is worth a look as it has slightly less impressive M36 and M38 to compare nearby and might give a idea of the variety you get.

Cartes du Ciel is a great way of understanding scale (and individual star magnitudes in many cases).

Hope that helps!