Messier 10 — Globular Cluster in Ophiuchus
NGC 6254
About M10
Description
M10 is a bright globular cluster in the constellation Ophiuchus, located about 14,300 light-years from Earth. It contains several hundred thousand stars and spans about 83 light-years in diameter. The cluster has an apparent size of about 20 arcminutes and shines at magnitude 6.4. M10 has a moderately dense core with a concentration class VII. Compared to its neighbor M12, which lies only 3.4 degrees away, M10 is noticeably more compact and concentrated.
Observing Tips
Located roughly midway between the stars Zeta and Beta Ophiuchi. At magnitude 6.4, it is faintly visible to the naked eye under excellent skies and easy in binoculars as a round glow. A 4-inch telescope at 100x shows a bright, concentrated core surrounded by a misty halo. Apertures of 6-8 inches resolve stars in the outer regions. Often observed as a pair with M12, which sits just 3.4 degrees to the northwest. Best viewed from June through August.
History
Discovered by Charles Messier on May 29, 1764. William Herschel resolved it into stars in 1783, and described it as 'a beautiful cluster of extremely compressed stars.' It was one of several globular clusters Messier discovered in Ophiuchus during the summer of 1764.
Fun Facts
M10's core has undergone core collapse and re-expansion, leaving it with a relatively dense center. The cluster has lost most of its lower-mass stars over billions of years through tidal interactions with the Milky Way. X-ray observations have revealed several binary star systems within the cluster.
Observe
1Properties
Position & Identifiers
2How easy to spot?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Easy | Easy | Easy |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
3Visibility
Set a location in User Settings to see visibility data.
4
Eyepiece View
5
Best Magnification
6Metallicity
[Fe/H] = -1.56 — these stars formed from gas about 36× poorer in iron than the Sun.
7Concentration class
Shapley-Sawyer class V — moderately concentrated core.
Explore
8
Classification Decoder
Discover
9
Light Travel Time Machine
10
Relativistic Travel
Community Photos (1)
Credit: Manfred Höcherl. License: CC BY-SA 4.0. (Wikimedia Commons)
Skybred Feb 28, 2026
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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