M10

This prominent 7th mag globular cluster in the constellation Ophiuchus has a size of about 20 arcminutes in diameter in deep photographs, more than 2/3 of the diameter of the full moon. At its distance of 14.500 light years, that corresponds to a linear diameter of about 80 light years. Its bright core, however, is less than half as large. It is receding at 69 km/s.

M12 and M14 are two other prominent globular clusters in Ophiuchus.

Exposure Data

Instrument: Intes Micro 8" f/6 Maksutov-Newton
F/stop: 6.0
Exposure: R: 4 min, G: 5 min, B: 4.5 min
CCD: ST-402
Date: May 22, 2006
Exposure start: 2:03 MESZ
Location: O2O Observatory, Mistelbach, Lower Austria
Conditions: Visual limiting magnitude 5.3 mag, no wind, moderate to heavy dew
Autoguider: ST-7E
Enhancement: CCDSoft, Adobe Photoshop, SGBNR - by Howdii

Observing Hints

M10 is situated at the very center of the constellation Ophiuchus, without any bright stars for orientation nearby. It is, however, not difficult to find the cluster, if you try a sort of methodical approach. In the western part of Ophiuchus a prominent pair of stars, Delta and Epsilon, is easily found. Delta is the upper (more northern) of the pair. If you first center it in your scope and then move 1/4 degree to the south, and from there 10 degrees due east, you will see M10 as fuzzy "star" in your finderscope. About one degree further east is a 5th magnitude star, which might help for orientation.

The brightest stars of M10 are about 11th magnitude, making them resolvable in a 4" scope. For better resolution 6" or 8" of aperture is recommended. Smaller telescopes won't show much detail in M10. For getting a nice view of the globular cluster a 10" or bigger scope should be utilized.

When observing M10, don't forget about M12, another prominent globular in Ophiuchus 3.5 degrees to the northwest...

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