Messier 26 | Universe Today

Written by Tammy Plotner

Object Name: Messier 26
Alternative Designations: M26, NGC 6694
Object Type: Open Galactic Star Cluster
Constellation: Scutum
Right Ascension: 18 : 45.2 (h:m)
Declination: -09 : 24 (deg:m)
Distance: 5.0 (kly)
Visual Brightness: 8.0 (mag)
Apparent Dimension: 15.0 (arc min)

Locating Messier 26: Finding Messier 26 in binoculars is easy as far as location goes – but not so easy distinguishing it from the starfield. Begin with the constellation of Aquila and its brightest star – Alpha. As you move southwest, count the stars down the Eagle's back… When you reach three you are at the boundary of the constellation of Scutum. While maps make Scutum's stars appear easy to find, they really aren't. The next most easily distinguished star in the line in Alpha Scutii. Aim your binoculars or finderscope there and you'll see northern Epsilon and southern Delta to the east. Messier 26 is slightly southeast of Delta and will show as a slight compression in the starfield to small binoculars and resolve a few individual stars to larger ones. In a finderscope, it will be a very vague brightening – perhaps not seen at all depending on your finder's aperture. In even a small telescope, however, you'll be pleased with what you see! Medium magnification will light up this 8th magnitude galactic star cluster and mid-sized instruments will fully resolve it.

What You Are Looking At: When this cloud of stars formed some 89 million years ago, it was probably far more compact than today's size of a 22 light year span. At a happy distance of about 5,000 light years from our solar system, we can't quite see into the nucleus to determine just how dense it may actually be because of an obscuring cloud of interstellar matter. However, we do know a little bit about the stars contained within it. "The relations between color and apparent magnitude show that NGC 6694 contains a well-defined main sequence and a slight indication of a giant branch." says James Cuffey, "A zone of low star density 3' from the center of NGC 6694 is noted. The ratio between general and selective absorption is estimated from the available data on red color indices in obscured clusters. Although uncertain in many cases, the results tend to confirm the ratio predicted by the law of scattering."

However boring a field of stars may look upon first encounter, studies are important to our understanding how our galaxy evolved and the timeline incurred. "Star Clusters are unique because all of the stars in the cluster essentially have the same age and are roughly the same distance from Earth." says Kayla Young of the Manhasset Science Research team, "Therefore, the purpose was to determine if a correlation exists between mean absolute magnitude and age of a star cluster. The absolute magnitude for star cluster NGC 6694 was calculated to be about 1.34 + .9. Using the B-V (Photometric Analysis) data ages were also calculated. After a scatter plot was created, the line of best fit demonstrated an exponential relation between the age and absolute magnitude."

History: While Messier Object 26 won't be impressive in binoculars – remember that it's much the same view that Charles himself got when he discovered it on the night of June 20, 1764: "I discovered another cluster of stars near Eta and Omicron in Antinous [now Alpha and Delta Scuti] among which there is one which is brighter than the others: with a refractor of three feet, it is not possible to distinguish them, it requires to employ a strong instrument: I saw them very well with a Gregorian telescope which magnified 104 times: among them one doesn't see any nebulosity, but with a refractor of 3 feet and a half, these stars don't appear individually, but in the form of a nebula; the diameter of that cluster may be 2 minutes of arc. I have determined its position with regard to the star o of Antinous, its right ascension is 278d 5' 25", and its declination 9d 38' 14" south."

Later, Bode would report a few stars with nebulosity – a field that simply wouldn't resolve to his telescope. William Herschel would spare it but only a brief glance, saying: "A cluster of scattered stars, not rich." While John Herschel would later go on to class it with its NGC designation, it was Admiral Smyth who would most aptly describe M26 for the true galactic cluster we know it to be…

"A small and coarse, but bright, cluster of stars, preceding the left foot of Antinous, in a fine condensed part of the Milky Way; and it follows 2 Aquilae by only a half degree. The principle members of this group lie nearly in a vertical position with the equatorial line, and the place is that of a small pair in the south, or upper portion of the field [in telescope]. This neat double star is of the 9th and 10th magnitudes, with an angle [PA] = 48 deg, and is followed by an 8th [mag star], the largest [brightest] in the assemblage, by 4s. Altogether the object is pretty, and must, from all analogy, possess affinity among its various components; but the collocation and adjustment of these wondrous firmamental clusters, and their probable distances, almost stun our present faculties. There are many astral splashes in this crowded district of the Galaxy, among which fine specimens of what may be termed luminiferous ether, are met with."

Power up! See how many stars you can – and can't – resolve in this dusty, curtained, distant beauty!

Top image thanks to Palomar Observatory, courtesy of Caltech and color image thanks to Hillary Mathis, Vanessa Harvey, REU program/NOAO/AURA/NSF.

Filed under: Astronomy