Messier 21
From DeepSkyPedia
| M 20 << Messier 21 >> M 22 Cr 362 << Collinder 363 >> Cr 364 Mel 187 << Melotte 188 >> Mel 189 | |
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| Position (epoch J2000) [1] | |
| Constellation | Sagittarius |
| Position | Ra 18:04:13.4 Dec -22:29:24 |
| DSS images | |
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Appearance [1] | |
| Apparent mag. | 5.9 |
| Size | 15' |
| Class | I 3 r |
| Stars | |
| Dreyer's description | Cl pRi lC st 9...12 |
| Other | |
| Other designations | M 21, NGC 6531, Collinder 363, Cr 363, Melotte 188, Mel 188, Lund 806, OCL 26 and ESO 521-SC019 |
| Notes | |
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Messier 21 is an open cluster in Sagittarius.
[edit] How to find it
[edit] Appearance
M 21 shows quite a strong concentration toward its center. It has cca 50-60 stars with wide range of brightness. [2]
[edit] Naked eye
Using naked eye, under 6.5-mag skies, Messier 21 can be seen as a patch of light, somewhat less bright than neigbouring M 22, M 17, M 6 and M 7. Since M 20 is just 40' to the SW, it is possible that combined light of both objects makes them visible to the naked eye. No other details are visible[3]
Under 6.9-mag skies, M 21 apears slightly less bright than nearby M 20. Close pair of 7-mag and 8-mag stars in the cluster's center may appear as a brightening within the cluster's glow.[4]
More reports:
[edit] Telescopes up to 70mm, binoculars up to 50 mm, and finders
This cluster looks diffuse in 7x35 binoculars.[5]
[edit] Telescopes 71mm - 100mm (2.8" - 3.9"), binoculars 51mm - 70mm
At lower power (12x to 20x), the cluster might look diffuse (globular-like) or partialy resolved.[6][5]
At higher power, like 60x, cluster is almost fully resolved. The only exception might be few stars in very dense central part.[7]
[edit] Telescopes 101mm - 141mm (4" - 5.5"), binoculars 71mm - 100mm
In 100mm- to 120-mm telescopes, at low power (21x), only some glittering can be seen around one bright star can be seen. The cluster is very inconspicuous.[8] At 28x, 8 stars inside 3' can be resolved, with southern part being somewhat more compressed.[9] Going up to 36x will show around 12 stars, even in very light polluted areas.[10]
At 107x, cluster is still very compressed, and some 15 stars can be seen in the central 4' area og the cluster.[11]
More reports:
[edit] Telescopes 141mm - 177mm (5.6" - 6.9")
A 6" telescope, at 75x, in very good conditions, will show somewhat scattered group of cca 30 stars.[12]
[edit] Telescopes 178mm - 234mm (7" - 9.2")
[edit] Telescopes 8" and above
In 8" telescopes, the central part of the cluster is condensed, but outer parts are very sparse. Up to 25[6] stars can be seen even under 5-mag skies. A few stars in the center, 2[4] to 5[6] of them, are much brighter than the rest. This aperture will propably enable you to see blue[6][13] color of brighter stars. The shape of the cluster resembles arowhead[13] or semicircle with opening to the north.
A 12" or 13" telescope will show compact group of moderately bright to bright stars. Number of resolved stars may rise to almost 50.[12]. The brightest cca 20 stars are arranged in 2 diverging rows of stars going to the W and EN, and an arc of stars to the N.[14]
More reports:
- Messier 21 observation by David Erzeel @ deepskylog.be (with Sky-Watcher 10" dobson (250 mm)) [include this report]
- Messier 21 observation by Tom Polakis with 13" and 20" [include this report]
[edit] Notes
[edit] References
- ↑ 1.0 1.1 Historic NGC and IC by Wolfgang Steinicke (version Nov. 20, 2006.)
- ↑ SEDS: Messier 21
- ↑ . M 16, M17, M 24, M 25 , M 20, M8, M22, M6, M 7, M 21 , Tudorica Alexandru , naked eye , 05/06.09.2004 , Ghirdoveni, Romania , LM: 6.5
- ↑ 4.0 4.1
Messier 20 and Messier 21 (sketch and report) , Jaakko Saloranta , naked eye and 8" Orion SkyQuest @ 38x + O-III , 16./17.4.2004 , Base del Teide, Tenerife, Spain (2280m) , LM: 6.9 - ↑ 5.0 5.1 x.astrogeek.org , Jeff Burton , Bushnell Falcon 7x35mm Binoculars, Bushnell GlassesOn 10x50 Binoculars, Orion Little Giant II 20x70mm Binoculars , May 15, 2001 , Paducah, KY, USA , LM: 4.0 - 4.5 , seeing: 8/10
- ↑ 6.0 6.1 6.2 6.3 x.astrogeek.org , Jeff Burton , Celestron Wide View 80mm Refractor, Meade LX200GPS 203mm SCT , 15x, 111x , June 9, 2002 , Golden Pond Observatory, KY, USA , LM: 5.0 , seeing: 6/10
- ↑
M 21 (sketch and report) , Jaakko Saloranta , Refractor Konus , d=3" , f=3" , 60x , 17./18.4.2004 , Base del Teide, Tenerife, Spain , LM: 7.0 , seeing: 2
- ↑ (IAAC) M5, M9, ... M21, ... M11 (Southern sky tour) , Martin Baur , Astroscan 4.1" f/4.2 Widefield (f/4.2) , d=4.1" , f=cca 17.22" , 21x , 30.06/01.07.2000 , near Hofgeismar, Germany , LM: ~5.0
- ↑ M 21 with 120mm f/8.33 refractor, eq. mount (Konus, Lukrica) by Ante Perković (SEEN, Jul 17 2004) [include this report]
- ↑ (IAAC) M80, M19, M62, M21 , Erhan Ozturk , Equatorial Newtonian f/8 , d=4.5" , f=36" , 36x , 9th June 1999 , Ankara, Turkey , LM: 3.5 , seeing: 3/10 (1 best)
- ↑
Messier 21 (sketch and report) , Iiro Sairanen , Newton , d=110mm , f=110mm , 107x , 18/19.4.2004 , Base del Teide (h=2280m), Tenerife, Spain , LM: 7.0 , seeing: 3
- ↑ 12.0 12.1 Sagittarius by Steve Coe - M 21 , Steve Coe , 6" f/6, 13.1" f 5/6 , 75x, 100x
- ↑ 13.0 13.1 (IAAC) M21 , William L. Schart , Celestar SCT, fork mount , d=203mm , f=2030mm , 58x, 80x, 120x, 170x, 203x , filter(s): none , 7/21/01 , Killeen, TX (Lat 31° 07' N, Elev 600 ft) , LM: 4.0 , seeing: 7/10
- ↑ (IAAC) M21 (NGC 6531) , Dave Mitsky , 12.5" f/6.5 Cave equatorial Newtonian , 121x , 6/18/98 , ASH Naylor Observatory, Lewisberry, PA (40.1° N) , LM: ~5.0 , seeing: 8/10
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