Messier 10

Messier 10
Like many of the most famous objects in the sky, globular cluster Messier 10 was of little interest to its discoverer: Charles Messier, the 18th century French astronomer, catalogued over 100 galaxies and clusters, but was primarily interested in comets. Through the telescopes available at the time, comets, nebulae, globular clusters and galaxies appeared just as faint, diffuse blobs and could easily be confused for one another. Only by carefully observing their motion — or lack of it — were astronomers able to distinguish them: comets move slowly relative to the stars in the background, while other more distant astronomical objects do not move at all. Messier’s decision to catalogue all the objects that he could find and that were not comets, was a pragmatic solution which would have a huge impact on astronomy. His catalogue of just over 100 objects includes many of the most famous objects in the night sky. Messier 10, seen here in an image from the NASA/ESA Hubble Space Telescope, is one of them. Messier described it in the very first edition of his catalogue, which was published in 1774 and included the first 45 objects he identified. Messier 10 is a ball of stars that lies about 15 000 light-years from Earth, in the constellation of Ophiuchus (The Serpent Bearer). Approximately 80 light-years across, it should therefore appear about two thirds the size of the Moon in the night sky. However, its outer regions are extremely diffuse, and even the comparatively bright core is too dim to see with the naked eye. Hubble, which has no problems seeing faint objects, has observed the brightest part of the centre of the cluster in this image, a region which is about 13 light-years across. This image is made up of observations made in visible and infrared light using Hubble’s Advanced Camera for Surveys. The observations were carried out as part of a major Hubble survey of globular clusters in the Milky Way. A version of this image was entered into the Hubble’s H

Messier 10 is notable for its high population of blue stragglers, which are stars that appear to be far younger than their neighbors. These stars in globular clusters are thought to have formed and aged together, so they should all be roughly the same age; however, these anomalous, bluer stars were created either by collisions between stars or other stellar interactions.

Visible From Pacific Northwest
Best Time To ObserveJuly
Minimum Size Of Viewing Device
Object TypeGlobular Cluster
DesignationsMessier 10, M10, NGC 6254, GCl-49
Right Ascension16h 57m 8.92s
Number Of Stars100,000
Apparent magnitude +6.4
Apparent dimensions 20′
Object Radius41.6 light years
Distance From Earth14,300 light years


The object was discovered by the French astronomer Charles Messier on May 29, 1764, who cataloged it as number 10 in his catalogue and described it as a “nebula without stars”. In 1774, German astronomer Johann Elert Bode likewise called it a “nebulous patch without stars; very pale”. Using larger instrumentation, German-born astronomer William Herschel was able to resolve the cluster into its individual members. He described it as a “beautiful cluster of extremely compressed stars”. William Parsons, 3rd Earl of Rosse thought he could distinguish a dark lane through part of the cluster. The first to estimate the distance to the cluster was Harlow Shapley, although his derivation of 33,000 light years was much further than the modern value.

Locating M10 In The Sky

Messier 10 can be found by astronomers by looking roughly half a handwidth west of the bright star Beta Ophiuchi, which is also known as Cebalrai, with Messier 10 lying a bit lower in the sky, to the south of M12. M10 lies along the line from Cebalrai to Zeta Ophiuchi, the third brightest star in Ophiuchus. It is only a degree away from 30 Ophiuchi, an orange giant star with an apparent magnitude of 4.83.

Viewing M10

small telescopes (3-inch) reveal about half the cluster’s size – roughly 8 to 9 minutes of arc – and its bright central region, which spans roughly 35 light years. 6-inch or 8-inch telescopes show the cluster extending across 15.1 arc minutes and reveal a large, bright central core. Meanwhile, deep images reveal M10 to span some 20 arc minutes of apparent sky and resolve stars across the entire area of the cluster.

Photographing M10

For those who are looking too photograph M10, the good news is that it is indeed possible using a DSLR. Using a camera similar to a Canon Rebel T2i with a Baader UV/IR filter, one can obtain a beautiful photo of M10 using only 2 shots at 300s each, with f/2.8, and ISO 800.

Sources And Further Reading

Descriptions of all of Messier Objects can be found here.

2 Comments on "Messier 10"

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