MikeBOKC
Post Laureate
Reged: 05/10/10
Loc: Oklahoma City, OK
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M22
#5318840 - 07/15/12 12:44 PM
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Touring some of the favorite globs at the club dark site last night with my CPC1100, I kept returning to M22, which has long been my number one. I wondered why . . . and then after scanning some of he summer highlights ike M13 and M5, I realized the difference: most globs float in space, but M22 is embedded in an already-rich star field down in Saggitarius, as if someone had already spilled a few hundred diamonds and then added a heap of a thousand more. I expanded my view from the Ethos 13 to the Brandon 48mm eyepiece and marveled at the spectacle. Nice weather in the summer is great, but M22 makes it extra special. Wonder what it would look like from a planet a couple of hundred light years away?
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Achernar
Postmaster
Reged: 02/25/06
Loc: Mobile, Alabama, USA
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Re: M22
[Re: MikeBOKC]
#5319003 - 07/15/12 03:02 PM
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M-22 is one of my favorite globular clusters. Through my 15-inch I can see an overall reddish-orange tint and numerous red stars in it too. To me it breaks up into stars more noticeably than M-13 through my 6-inch as well. It still looks like a pile of sugar or fine sand on a dark piece of velvet all the same.
Taras
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Dave Mitsky
Postmaster
Reged: 04/08/02
Loc: PA, USA, Planet Earth
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Re: M22
[Re: Achernar]
#5319056 - 07/15/12 03:59 PM
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M22 is one of the brightest (magnitude 5.1) and closest (10,600 light years) globular clusters. It's also one of just four globular clusters known to contain a planetary nebula (GJJC1). M22 is a stunning target from the southern hemisphere.
Dave Mitsky
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Matt2003
Post Laureate
Reged: 04/22/10
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Re: M22
[Re: Dave Mitsky]
#5319291 - 07/15/12 07:39 PM
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M.22 is also my favorite, seeing as Omega Centauri is too low for a really good look (its still great though, but I'd love to see it close to zenith. Then it would be breathtaking!). And not just because of its brightness. Its also very easy to resolve nearly across the core in an 8 inch scope.
Clear Skies,
Matt
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John K
Carpal Tunnel
Reged: 12/26/05
Loc: Vernon BC Canada
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Re: M22
[Re: Matt2003]
#5319650 - 07/15/12 11:49 PM Attachment (31 downloads)
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Last year I had some fun with M22 sketching it.It really is a special globular as you stated.I also like M71 for the same reasons as above.
Here is the sketch from last year with my 15" scope.
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Feidb
Pooh-Bah
Reged: 10/09/09
Loc: Nevada
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Re: M22
[Re: John K]
#5319680 - 07/16/12 12:35 AM
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It has always been my favorite globular, bar none. I even take it over M-13 and the propeller. I looked at it two weekends ago and even though it was above the skyglow of Las Vegas, it still looked great. Even my grandson, who is 7 knows it well.
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stevecoe
"Astronomical Tourist"
Reged: 04/24/04
Loc: Arizona, USA
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Re: M22
[Re: John K]
#5319689 - 07/16/12 12:41 AM
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I have a rather unique observation of M 22. I would love to see this happen again.
M 22 13" f/5.6 Sentinel, Az. S=7 T=8 38mm Erfle 60X-- on 14 Sept. 1996, Jupiter is in the field of view with this excellent globular, a unique observation. 4 bands are seen on Jupiter and the moons are 3 on one side and 1 on the other around Jupiter. Also, there are 50 stars resolved on M22, even at this low power. 220x--64 stars counted in NW quadrant for a total of appoximately 250 stars resolved. I see this cluster as very bright, very large, very rich, very much compressed, much, much brighter middle and round. There is a beautiful chevron of 7 stars on the NE side. 330X--is a great view, there are several dark lanes on the north side. Most of the stars are white, a few are light yellow.
Clear skies to us all;
Steve Coe
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C_Moon
Pooh-Bah
Reged: 10/23/09
Loc: Virginia
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Re: M22
[Re: stevecoe]
#5319716 - 07/16/12 01:23 AM
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I have a rather unique observation of M 22. I would love to see this happen again.
M 22 13" f/5.6 Sentinel, Az. S=7 T=8 38mm Erfle 60X-- on 14 Sept. 1996, Jupiter is in the field of view with this excellent globular, a unique observation. 4 bands are seen on Jupiter and the moons are 3 on one side and 1 on the other around Jupiter. Also, there are 50 stars resolved on M22, even at this low power. 220x--64 stars counted in NW quadrant for a total of appoximately 250 stars resolved. I see this cluster as very bright, very large, very rich, very much compressed, much, much brighter middle and round. There is a beautiful chevron of 7 stars on the NE side. 330X--is a great view, there are several dark lanes on the north side. Most of the stars are white, a few are light yellow.
Clear skies to us all;
Steve Coe
Wow, must've been amazing. I just "re-lived" it on Skytools 
Sadly, my calculations w/ ST3 show it won't happen again (and actually be visible) until April 2055.
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reiner
sage
Reged: 09/28/05
Loc: Freiburg, Germany
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Re: M22
[Re: Achernar]
#5319752 - 07/16/12 02:10 AM
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Through my 15-inch I can see an overall reddish-orange tint and numerous red stars in it too.
Hi Taras,
this is a very interesting observation. I second on it, though M22 is very low from my 48° N latitude and I can see this only on very transparent nights. I have not noticed such color with M13. I guess it has to do with distance. M22 is one of the close globulars, while most other bright globulars are much more distant (with the exception of M4, which is even further S, however :-( ). The brightest stars in M22 have mag 10.7, while those in M13 or M15 are mag 11.9 and 12.6, respectively. The brightest stars in M22 are probably just bright enough to stimulate color vision, while those of M13 or M15 are still below that threshold (all depending on aperture as well, of course).
Has anybody else experienced such a color difference between globulars?
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csa/montana
Den Mama
Reged: 05/14/05
Loc: montana
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Re: M22
[Re: reiner]
#5319972 - 07/16/12 09:55 AM
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I have not noticed such color with M13.
With my first session with my new 16"; I came to M13, and was astonished with the bluish tint it had! I'd never seen any "color" with my 8"!
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star drop
Snowed In
Reged: 02/02/08
Loc: Snow Plop, WNY
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Re: M22
[Re: reiner]
#5320129 - 07/16/12 11:16 AM
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Has anybody else experienced such a color difference between globulars?
On steady night I can easily see the red giant stars in several globular clusters with a 25" telescope at magnifications of 98.5x and up. On turbulent nights the color seems to smear across the easily resolved globular clusters making it possible to compare their color to unresolved ones. A few years back someone else asked about this and I compared several clusters that are visible at this time of the year and found that M15 appeared the reddest of my small sample. I picked clusters that were close to the same distance from the zenith. This test was based on memory as it takes a bit of time to manage a ladder and acquire each object manually but I think that I was fairly accurate.
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reiner
sage
Reged: 09/28/05
Loc: Freiburg, Germany
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Re: M22
[Re: star drop]
#5320294 - 07/16/12 12:54 PM
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That's interesting! Did you look at the brightest stars or at the overall color of the globular?
I have noticed reddish stars only in M22 up to now. Seems I have to check this again.
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star drop
Snowed In
Reged: 02/02/08
Loc: Snow Plop, WNY
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Re: M22
[Re: reiner]
#5320339 - 07/16/12 01:16 PM
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That's interesting! Did you look at the brightest stars or at the overall color of the globular?
I have noticed reddish stars only in M22 up to now. Seems I have to check this again.
I was looking at the overall color of the globular clusters. Defocusing the clusters doesn't work as well as poor seeing does. I presume that the image motion generated by the poor seeing is helping here. The clusters range from greyish white to creamy yellow under these conditions.
On steady transparent nights the reddish stars (actually they look orange to me) are visible in at least M13, M15 and M22. That is at around 100x and I haven't experimented much with color fading at higher magnifications. My biggest problem is getting any really decent sky conditions and when that happens there is so much else to see that I forget about color detection unless if it pokes me through the eyepiece.
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Matt2003
Post Laureate
Reged: 04/22/10
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Re: M22
[Re: star drop]
#5320574 - 07/16/12 03:14 PM
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OK, now I have a short-time project I can do, see if I can dectect the colors of some of the red giants in GCs like M.22, M.4, M.13.
Up until now, I have only ever seen the slightest tint of yellow. Most globs in my 8 inch lokk white or bluish.
Clear Skies,
Matt
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GlennLeDrew
Postmaster
Reged: 06/18/08
Loc: Ottawa, Ontario, Canada
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Re: M22
[Re: Matt2003]
#5324218 - 07/18/12 10:17 PM
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The mean colors of globulars mostly range from whitish F- to yellowish-white G-types based on spectroscopy. The brightest stars are reddish giants. For many clusters there is a bit of an increase in numbers of stars of similar brightness on the bluish horizontal branch. The more populous and/or concentrated clusters have the bulk of unresolved starlight coming from main-sequence and turnoff-region stars of whitish G-types.
So it's to be expected that clusters well enough above the reddening near-horizon atmosphere and not suffering the reddening effects of interstellar extinction will mostly look like a whitish or yellowish, with the brightest stars orange-ish. Through really big apertures, the bluish HB stars may have their color discernible.
To imagine the naked eye appearance of a globular as seen from much closer up, simply gaze into a low power eyepiece which delivers an exit pupil at least near your own maximum pupil diameter. Note the magnification, and divide the cluster's distance by this. For example, if the cluster is 10,000 l-y distant and the magnification is 100X, you are seeing the cluster very nearly as it would be seen naked-eye from only 100 l-y. The numbers of stars and their apparent brightness are very representative of that imaginary spacecraft view.
Another way to appreciate this. The apparent diameter of a spherical agglomeration is near to 90 degrees when seen at a distance from the center equal to the group's diameter. Globulars are typically 150 l-y across, and so if a globular (including the sparser outer 'halo', not just the prominent core) fills the field of a Nagler or Ethos eyepiece, you're effectively located as far from the cluster center as its diameter.
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Matt2003
Post Laureate
Reged: 04/22/10
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Re: M22
[Re: GlennLeDrew]
#5325726 - 07/19/12 08:00 PM
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Neat trick to imagine approaching them in a spacecraft! Since M.22 is closer than 10,000 LY. how close would you estimate my view can be?? Or maybe that chain of giants across M.4?
Clear Skies,
Matt
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GlennLeDrew
Postmaster
Reged: 06/18/08
Loc: Ottawa, Ontario, Canada
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Re: M22
[Re: Matt2003]
#5327152 - 07/20/12 04:25 PM
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Matt,
You mentioned an 8" scope in an earlier post. An exit pupil of 6mm means a magnification of 34X. So your scope simulates your naked eye view of an object as would be seen from a distance 1/34 the Earth-object distance.
You can crank the power up, of course, to effectively move closer. Just be aware that the smaller exit pupil darkens the view. For example, if you double the magnification to 68X, the 3mm exit pupil makes the surface brightness of a nebula, galaxy or unresolved cluster core 1/4 as bright. in reality, the surface brightness will remain constant as your distance changes. And for resolved stars, the extra magnification will reveal somewhat fainter ones due to the darkening of the sky, but the gain here is much smaller than the 4X (1.5 magnitude) fainter stars you would see by moving twice as close.
These are the reasons why I suggest sticking to a near-to-eye pupil sized exit pupil when desiring to simulate the naked eye view from a much closer location. It's now apparent that the distance ratio depends on the ratio of objective to eye pupil diameter. If the observer's pupil opens to 6mm, a 60mm scope will 'bring' him 10X nearer to the object (when used at a 6mm exit pupil and 10X.) A 600mm (24") aperture will bring him 100X nearer.
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: M22
[Re: GlennLeDrew]
#5327192 - 07/20/12 04:53 PM
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It's now apparent that the distance ratio depends on the ratio of objective to eye pupil diameter. If the observer's pupil opens to 6mm, a 60mm scope will 'bring' him 10X nearer to the object (when used at a 6mm exit pupil and 10X.) A 600mm (24") aperture will bring him 100X nearer.
Interesting... According the Sky Safari, M22 is about 10,000 light-years so the old pea shooter at the lowest power (~100x with a 6.36mm exit pupil) would simulate naked eye at 100 light years.
According to Wikipedia, M22 is 10,600 light-year away and about 99 light years in diameter, that's slightly bigger than the moon.
At 100 light years, it would cover over 50 degrees of the sky.
That is a challenge to get a grasp on what that would be like.
Jon
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Matt2003
Post Laureate
Reged: 04/22/10
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Re: M22
[Re: Jon Isaacs]
#5328371 - 07/21/12 02:34 PM
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It would be breathtaking, that is what that view would be! LOL
Thanks Glen, I got a chance to view this oldes friend of globs (first one I ever observed in a 6 inch Reflector)thursday night. Brought back many memories! All good, but the view in my 8 inch is still the best of all!
Clear Skies,
Matt
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jeff heck
Pooh-Bah
Reged: 01/16/06
Loc: stl,mo.
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Re: M22
[Re: Matt2003]
#5328652 - 07/21/12 06:10 PM
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I got my first view of M22 in the new 16" at a very darksite this week. Like Mike exclaims on the American Pickers tv show...OH MY GOD!  I saw a faint yellowish tint throughout the cluster.
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