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Binocular Universe: Orion's Arm

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#1 Charlie Hein

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Posted 01 January 2013 - 09:37 AM

Binocular Universe: Orion's Arm

By Phil Harrington

#2 Mark9473

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Posted 04 January 2013 - 06:53 AM

Another nice one, Phil. I really should spend more time in that region of the sky, but in this season clear nights are scarce and the attractions of the winter sky are many.

Any idea what magnification it takes to start seeing the 37 in the 37-cluster (NGC 2169)?

#3 JakeSaloranta

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Posted 04 January 2013 - 07:25 AM

If you want to be precise, NGC 2175 is an emission nebula rather than an open cluster and for some reason, this little error still lingers on. If you look at the original discovery notes for NGC 2175, there is no mention of a cluster but simply a "*8m in neb". The cluster "NGC 2175" is Collinder 84.

/Jake

#4 PhilH

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Posted 04 January 2013 - 07:26 AM

Thanks for pointing that out, Mark. I probably should have acknowledged the "37" configuration in NGC 2169, even though it's not readily visible through low-power binoculars.

But you raise a good question about the min magnification (and aperture) needed to resolve the pattern. I have never noticed in in my 16x70s and in all honesty have never viewed it through my 25x100s. If I get a chance to this season, I'll post my results here.

I'd also invite you and others to do likewise and see how our results compare. I'd be particularly in your view through your 15x60s and 15x63s.

#5 PhilH

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Posted 04 January 2013 - 08:22 AM

If you want to be precise, NGC 2175 is an emission nebula rather than an open cluster and for some reason, this little error still lingers on. If you look at the original discovery notes for NGC 2175, there is no mention of a cluster but simply a "*8m in neb". The cluster "NGC 2175" is Collinder 84.

/Jake


Jake,

Actually, according to Dr Harold Corwin's exceptional NGC/IC Project web site, NGC 2175 and Collinder 84 are one and the same, even though there is no mention of the cluster per se in the discovery notes.

NGC 2175 is a very large roughly circular emission nebula which also includes NGC 2174 and IC 2159 (both of which see), and a star cluster which has inherited the NGC number, though there is no mention of it in the discovery notes. The nebula is centered on SAO 078049, though the brightest knot (which Bigourdan took for N2175; hence, the ``corrected'' RA in the IC2 Notes) is about three arcmin to the west-northwest. Auwers's note makes it clear that NGC 2175 is much more than just the knot: he gives dimensions of 25 arcmin by 8 arcmin, and specifically adopts the position of Lalande 11668 = SAO 078049 as that for the object. I have followed his lead. - Dr. Harold G. Corwin, Jr.

You can find his full description here: http://www.ngcicproj...s/dss_n2100.asp

#6 Mark9473

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Posted 04 January 2013 - 09:03 AM

I'd also invite you and others to do likewise and see how our results compare. I'd be particularly in your view through your 15x60s and 15x63s.


I'll be on it just as soon as the weather cooperates! Which may be a long while... :(

#7 JakeSaloranta

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Posted 04 January 2013 - 11:05 AM

Actually, according to Dr Harold Corwin's exceptional NGC/IC Project web site, NGC 2175 and Collinder 84 are one and the same, even though there is no mention of the cluster per se in the discovery notes.


Phil,

Both Wolfgang Steinicke (NGC/IC data 2012 "NGC 2175 = emission nebula") and Archinal (Star Cluster-book page 118: "... clearly the the name NGC 2175 should be assigned to the nebula only") have it only as a nebula. But many researchers, many versions I suppose. I'm personally gonna stick with the original discovery note by Bruhns/Auwers. I'm uncertain how old Corwin's notes are on this (supposedly older than those of Archinal and Steinicke) but I suppose I understand the urge to fuse both the cluster and the nebula under the same designation. This of course then underminds Collinder's discovery of the cluster in the area.

/Jake






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