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cpsTN
professor emeritus
Reged: 04/26/07
Posts: 742
Loc: Smyrna, TN USA
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Over that last several days, I have been compiling a list of the Messier OCs and GCs for hunting. Somewhere in my workings, I have come across a variation in the number of clusters in some listings. I am getting either 27 or 30 OCs and 29 or 30 GCs. What could be the reason for this and is there any dispute as to what some of the Messiers are that might lead to varying counts. Can someone point me toward an acurate count of each type of Messier.
Also, Some lists I have found label M16 as a Nebula and others as an OC. Since both are present in M16, which one is it officially? Thank you all.
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Charles P. Sands
Zhumell 8" f/5.9 dob
Looking Up since 1982
The heavens declare the glory of God;
and the firmament sheweth His handywork
(Psalm 19:1)
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MikeRatcliff
Pooh-Bah
Reged: 06/12/04
Posts: 1107
Loc: Redlands, CA
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I don't think there is an "official" counting of object types.
I like the SEDS website SEDS Messier list organized by type
For open clusters, there is the complication you stated that some nebula have embedded open clusters. Other complications include M73 that is really a multiple-star, and M24 that is really a star cloud in the Milky Way. And M24 has a small embedded open cluster NGC6603 that Messier did not mean to be the entry.
Now globular clusters I thought there was not much confusion. SEDS only has 29. I would be curious to see what the 30th one might be. I recall some debate about M71 but it is generally considered a globular these days.
And there were questions about the total number. The SEDS website has a lot of good history and links.
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16" f/4.9 dob
Tele Vue Plossls 32,25,20,15,11
13 Nagler T6
10.5 Pentax XL
Brandon 32, 16
12.5 UO ortho, 9 Circle T ortho
2x TV Barlow
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Michael & Louise
member
Reged: 06/02/08
Posts: 11
Loc: Calgary, Alberta
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M8, M17 and M20 can also be considered to include clusters and most likely, although I don't have the info handy right now, Messier saw the clusters in M16 and M17 rather than the nebulae. I get 30 OCs and 29 GCs overall.
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Louise and Michael
Astronomical Sketches
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Tony Flanders
Carpal Tunnel
Reged: 05/18/06
Posts: 2098
Loc: Cambridge, MA, USA
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Quote:
M8, M17 and M20 can also be considered to include clusters and most likely, although I don't have the info handy right now, Messier saw the clusters in M16 and M17 rather than the nebulae.
All emission nebulae have embedded star clusters. That's what powers them to emit light. M42 is another really obvious example. You don't really think that the Trapezium is a quadruple (or hexuple) star, do you? It's a mini star cluster showing hundreds of members in deep photographic images.
In the case of M16, the star clusters is much more obvious than the nebulosity. M17 is just the opposite. Its star cluster is pretty much hidden inside the gas and dust, and really visible only in infrared images.
Conversely, all open star clusters used to be emission nebulae, and many of them still have some faint nebulosity hanging around. Open clusters and emission nebulae are really just two different aspects of the same category of objects.
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Tony Flanders
eyeglasses
6x15 and 8x32 monoculars
8x25, 7x35, 10x30 IS, 10x50, and 15x70 binoculars
70mm and 100mm achromatic refractors
4.5", 7", and 12.5" Dobs
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cpsTN
professor emeritus
Reged: 04/26/07
Posts: 742
Loc: Smyrna, TN USA
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Thank you, Tony. That is an insight that I should have had by now, which tells me I need to pay more attention. A review of the emission nebulas should now be on the list. I will probably start finding OCs everywhere, now!
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Charles P. Sands
Zhumell 8" f/5.9 dob
Looking Up since 1982
The heavens declare the glory of God;
and the firmament sheweth His handywork
(Psalm 19:1)
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