Messier 10 (NGC 6254): Rich Cluster Close to the Galaxy’s Heart

Messier 10, also known as NGC 6254, is a bright globular cluster in the constellation Ophiuchus and is best viewed in July. M10 is one of 21 globular clusters and seven Messier objects in Ophiuchus.¹ So if you are stopping by to see this globular cluster, plan to stay a while to enjoy a good number of gems.

Messier 10 is considered one of the better globular clusters for amateur astronomers because of its bright 6.5 magnitude and dense center. These attributes make it viewable from suburbs with a smaller scope and even binoculars.

Beyond its “wow” factor, Messier 10 has several other notable features. For one, studies show M10 to be one of the youngest globulars in our galaxy based on the lack of heavy elements found in the cluster. Second, it lies pretty close to the center of the Milky Way. Its physical diameter is around 80 light-years and lies around 14,000 light-years away. These dimensions translate into a beautiful globular nearly two-thirds the diameter of the moon in the sky.

My Observations

After what seems the longest season of cold and dreary weather in the Pacific Northwest, tonight’s sky is clear and crisp. The heavens have been unfolding every minute in front of me. This is my first time sailing through the constellation Ophiuchus. Until tonight, I never realized the area to be so rich! M10’s bright and dense core makes it an enjoyable target, even under the suburban light dome of Seattle.

Key Stats

Constellation	Ophiuchus
Best Viewing	Summer
Visual Magnitude	+6.6
Absolute Magnitude	-6.6
Distance from Earth	14,000 ly
Diameter	83.5 ly
Apparent Size	20 arcmin
Milky Way Location	Near Norma
My Viewing Grade	B+

Historical Observations

May 26, 1764 observation by Charles Messier

“In the night of May 29 to 30, 1764, I have determined the position of a nebula which I have discovered in the girdle of Ophiuchus, near the 30th star of that constellation, of sixth magnitude. according to the catalog of Flamsteed. When having examined that nebula with a Gregorian telescope of 30 pouces which magnified 104 times, I have not seen any star there: it is round and beautiful, its diameter is about 4 minutes of arc; one sees it difficultly with an ordinary [non-achromatic] refractor of one foot [FL]. Near that nebula one perceives a small telescopic star. I have determined the right ascension of that nebula as 251d 12′ 6″, and its declination as 3d 42′ 18″ south. I marked that nebula in the chart of the apparent path of the Comet which I have observed last year [the comet of 1769].” ²

March 19, 1786 observation by William Herschel

“A beautiful, very rich, compressed cluster of stars of various magnitudes.“

Sources and Notes

M10 banner created from NASA image. Original image by ESA/Hubble and found on the following article: Garner, Rob. “Messier 10.” NASA, NASA, 6 Oct. 2017, https://www.nasa.gov/feature/goddard/2017/messier-10.

¹ OMeara, Stephen James. “Tackle a Globular Cluster Showdown.” Astronomy.com, 18 July 2019, https://astronomy.com/magazine/2019/07/tackle-a-globular-cluster-showdown#:~:text=With%2021%20globular%20clusters%2C%20Ophiuchus,M19%2C%20M62%2C%20and%20M107.

² Plotner, Tammy. “Messier 10 (M10) – the NGC 6254 Globular Cluster.” Universe Today, 4 Apr. 2016, https://www.universetoday.com/31328/messier-10/.

AKA: M10, NGC 6254