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Globular Clusters | |
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10-inch Newtonian, ST2000XM, 20:9:9:9 M29 is a medium size globular, extending well beyond its apparent size in this image. The accepted diameter is 13.8'. This field is 21.7' top-to-bottom, so the cluster covers almost 65% of that distance. The outer portions are basically lost in this rich Milky Way field. It is fairly concentrated and I could just barely resolve it in the core. There were strong, gusty winds throughout the time I was acquiring this image. I really appreciated the Sigma Clip stacking that Berry and Burnell provided with AIP4Win. Without it, I would have had to discard over half my sub-exposures. I use it routinely but it was essential for this image. |
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10-inch Newtonian, ST2000XM, 28:10:10:10 M92 is a wonderful globular that is often overlooked because of its proximity to M13. It is very dense and the image is just barely resolvable to the core, with a nice range of colors. It is a naked eye object under exceptional conditions.
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10-inch Newtonian, ST2000XM, 30:8:8:8 This is a good opportunity to compare M92 and M14 "side-by-side". M14 is a bit smaller, about a magnitude fainter, and less dense with fewer stars, compared to M92. Even so, they look quite similar. The surrounding star field for M14 is richer, as it is considerably closer to the main band of the Milky Way. This cluster has a large number of variables and is one of only two globular clusters which has produced a nova. |
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10-inch Newtonian, ST2000XM, 20:7:7:7 M107 is a loose globular cluster, resolvable to the center. It was probably the last Messier object to be discovered, and one of the last to be added to the list. It didn't make it until 1947. It appears to have a couple of darker obscured regions, especially toward the N (top), which are uncommon in globular clusters. The cluster itself is not particularly colorful, with a high percentage of white or near-white stars, but about two thirds the way from the cluster to the bottom of the field, slightly right of center, is one of the reddest stars I've ever seen in my imaging. |
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10-inch Newtonian, ST2000XM, 30:10:10:10 NGC 5897 is a large, bright, extremely loose globular cluster. It is significantly larger than M107, above, and even looser. Some of the densest open clusters are almost as concentrated but generally lack the symmetrical shape. It is very colorful compared to M107, with a high percentage of blue and yellow stars. |
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10-inch Newtonian, ST2000XM, 24:8:8:8 M56 is a very attractive globular cluster in Lyra. It is well resolved to the core and has a high concentration of yellow stars, although this color is probably partially due to obscuration by dust in the Milky Way. |
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10-inch Newtonian, ST2000XM, 18:6:6:6 M70 is a small, condensed globular in Sagittarius. It is in a very rich star field, and tends to be overlooked among the wonders of this area. It is a pretty object and well worth a look. M54, M69, and NGC 6652 are all nearby, within a single field of a fairly wide-field finder. |
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10-inch Newtonian, ST2000XM, 16:8:8:8 M75 is similar to M70 but even more condensed towards the core. This image, and the M70 image above, were made at exactly the same image scale and almost the same exposure. M75 appears to be larger and a little brighter but, in fact, the opposite is true. Measuring the size of a globular can be difficult since the star density declines gradually and determining which of the outlying stars are members requires a lot of careful research. And magnitude measurements can be skewed by a few bright stars. One aspect of the visual impression is more clear-cut: M70 is in a much richer star field. This is logical because M70 is close to the heart of the Milky Way while M75 is outside the generally mapped "edges". It is, of course, part of the galaxy but far enough from the plane to be outside the brighter parts of the disc. Because of this, several tiny background galaxies can be seen in the image. |
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10-inch Newtonian, ST2000XM, 22:8:8:8 M72 is one of the least impressive of Messier's globulars, especially visually, but is does make an attractive image. It is resolved to the core and shows a nice range of colors. It is a disappointment compared to the other M-globular in Aquarius, M2, which is one of the best. |
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10-inch Newtonian, ST2000XM, 21:15:12:11 M13 is one of the biggest and brightest globular clusters, especially for those in the northern latitudes, and a favorite for observers on summer nights. It can be seen as a hazy patch in binoculars or a finderscope, and shows more and more resolution into individual stars as larger telescopes are used. |
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Meade 2045D, ST2000XM, 48:32:28:26 minutes, 42' x 59' This magnificent globular cluster is perhaps THE favorite target at the Texas Star Party. Most attendees make sure to take at least one look every year, even if they have been observing it for 20 years. There is no other cluster which can compare. At first glance, it may appear that M13, above, is similar but this field is approximately twice as wide and high! It is not easy to get a decent image, however, since it never gets more than 13 degrees above the TSP horizon. Seeing can be a real problem but I got fairly lucky the night this image was made. |
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 NGC 6121 (M4) Meade 2045D, ST2000XM, 24:16:12:12 minutes, 46' x 62' M4 is one of the half dozen or so largest and brightest globular clusters. Comparing it with NGC 5139 emphasizes how extraordinary 5139 is. It dwarfs M4 and no other globular does that. This is another image from the 2009 TSP. I'm not sure what the fingers of nebulosity(?) entering the field in the NE and SE corners really are, but I doubt that they are "real". They were not caused by frost or dewing but are probably some kind of reflection from Antares, approximately 50' beyond the edge of the field. Faint nebulosity from IC 4604, which surrounds Antares, reaches almost to M4 but all images I've found indicate it is extremely thin and diffuse in this area. I'm fairly certain it has no structures with this kind of contrast in the field. But I decided not to crop them out just to show the kind of things which show up in images. |
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 M15 (NGC 7078) 10-inch Newtonian, ST2000XM, 22:24:18:18 minutes M15 is a very bright (6.0 magnitude), very concentrated globular cluster. It has one of the most densely packed cores of any Milky Way globular. |
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 10-inch Newtonian, ST2000XM, 20:20:20:20 minutes The globular cluster Messier 71 is resolvable all the way to the core. It has an attractive mix of blue, yellow, and orange stars, and is seen against the background of the Milky Way. |
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 10-inch Newtonian, ST2000XM, 20:14:14:14 minutes, 20.9' x 27' Messier 30 is large, bright, and
very concentrated. It is very difficult to resolve the core.
This image replaces a mediocre one that was on the site previously.
It has smaller, crisper stars and shows more resolution to the core. |
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NGC 6656 (M22) 10-inch Newtonian, ST2000XM, 34:22:20:20 minutes M22 is large, bright, and resolvable to the core. It has an attractive mix of star colors. It ranks second behind M13 for the brightest globular visible from mid-northern latitudes. It is also one of the nearest. Images made before and after my tube replacement were merged to produce this image, so it still shows traces of the defects typical of my older images. |
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NGC 6809 (M55) 10-inch Newtonian, ST2000XM, 10:10:10:10 minutes M55 is larger than M22 but is much less concentrated. It is even more easily resolved and gives the appearance, at least, of being resolvable visually in a moderate size scope. This image is a reprocessing of my previous data, to improve the color balance. |
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NGC7089 (M2) 10-inch Newtonian, ST2000XM, 10:10:10:10 minutes M2 is an extremely concentrated cluster. It is very hard to avoid over-exposing the core, and even harder to resolve it.
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