This month I am combining my two articles, At The Eyepiece, and Messier of The Month into one. Also known as the Sagittarius Star Cloud, M 24 has a somewhat confusing history due to a wrong R.A. assigned to it by Barnard. It wasn’t until 2001 that the mistake became well known, and Messier’s original discovery could be acknowledged (see the longer explanation at cseligman.com, under the IC 4715). There is only one other Messier object with an IC designation, that being M 25/IC 4725. Easily seen with the naked eye, M 24 is very large, extremely star-rich, and beautiful in binoculars and a joy in a rich field telescope, such as the Edmund Astroscan. While much of Sagittarius provides rich sweeping at low power, there is no denying the intensity of M 24.
While it appears stunning with any sort of visual aid, I spent over an hour here one September night in 2014 with a 12” Dob, exploring every nook and cranny of this colourful, star-filled area. Within the cloud are three other small open clusters, as well as a planetary nebula. So if you have some time to spend one fine summer or early autumn evening, M 24 is a recommended stop. The cloud’s size is given as 120’ of arc, so I began exploring with my lowest possible magnification, which is 43x. Oc 6603 is conspicuous right away. Immediately south of the cluster are 6 bright stars, arrow shaped. These stars appear to be involved with the richest and most splendid area, and seem to be at the heart of the cloud. The sweeping continues to be exceptional if moving south preceding to variable star V4387 (see map). A bright yellow star, V4387 leads south to another beautiful area of thousands of stars. Moving back to the original arrowhead, the star just south of oc 6603 is a deep orange. South following is a bright double star, yellow and blue, one of many doubles within the cloud. There is so much more to discover about the cloud itself, but I will move on to some of the other named points of interest.
Oc 6603 (Size 4’; Visual Mag. 11; brightest star mag. 14; 100 stars) is hazy, bright, and not too small at 43x. It looks so much like a comet that no wonder some people still mistake this cluster for M 24 itself. Even at 43x it begins to resolve. We were also able to resolve some of it in Deb’s 6” reflector at 125x. At 60x and 12” the cluster is still bright, and still in the beginning stages of resolving. At 100x there is some resolution all across the cluster, similar to that of a globular cluster. A bright line of unresolved haze runs through the middle, NE to SW. 125X gives decent resolution, with the central hazy bar narrowing. The cluster is finally fully resolved at 250x, including the bar, now seen as a line of tiny stars. There are dark patches on either side of the line, as well as many tiny stars. This object is a real beauty in a 12” scope!
Collinder 469 is a compact cluster ( Size 2.6’; Visual mag. 9.1; 15 stars) preceding oc 6603 by 2’ of R.A., and just a tiny bit north. I located it at 60x, noting several bright stars in a tight V-shape, with background haze. At 100x it is very compact, with few faint stars resolving. At 200x 15 stars can be counted, several being very faint.
Oc Mrk 38 (2’) shows three bright stars at 60x, one of them being yellow and quite bright. At 200x 10 stars are seen very close to the bright three, with a few others close by.
Planetary nebula 6567 lies just south preceding Mrk 38. At a minuscule size of only 12” of arc, the object appears virtually stellar at 250x. A tiny bit of fuzz can be discerned around it, being a grayish-blue colour. It is bright, at mag. 11, and I have seen it with an 8”. The central star is mag. 14.3, though it is washed out by the brightness of the haze.
While sometimes passed over for the wondrous nebulae and clusters in Sagittarius, M 24 is worth spending time exploring. I haven’t visited yet with Space Eye, my 2” refractor, but it’s on the list for summer. Clear skies.
Mapman Mike
