M10 (Globular Cluster)
A bright globular cluster in the middle of Ophiuchus, 3.3° from M12 and at almost the same distance. The two look alike in a telescope, but M10 is the heavier, at about 189,000 Suns against 106,000, and the poorer in heavy elements.
Globular cluster in Ophiuchus. Magnitude 6.6.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 79° above the southern horizon at its highest; from Lethem (3.4° N), to 82° above the southern horizon. It is highest at midnight on the night of 3 Jun, in the middle of its season. The page works out tonight's rise, highest point and set for both towns in Guyana time (UTC-4), and where the Moon is.
What you'll see
- Your eyes: Not visible to the eye. It lies 10.7° east of Yed Prior.
- 10x50 binoculars: A round glow, brighter towards the middle. M12 is 3.3° to the north-west.
- A small telescope (80 to 100 mm): A bright round glow with a dense middle; at 100x its edge breaks into stars.
- A camera: Tiny on camera: it needs 2,000 mm or more of focal length on a tracking mount.
How big, how bright, how far
- Size on the sky: 9.3′, 30% of the Moon's width (the Moon is about 31′ wide).
- Brightness: magnitude 6.6. Fainter than the faintest stars in Georgetown (4.3) and Lethem (6.0): binoculars or a telescope.
- Distance: 16,500 light-years. The light reaching your eye left it about 16,500 years ago.
- True size: 45 light-years across its catalogued outline; light crosses it in 45 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Globular cluster
- Mass
- About 189,000 times the Sun's mass
Measured: Which generation its red giants belong to (488 measured near its centre).
- Second generation: 63.6%, born from gas the first stars enriched
- First generation: 36.4%, ± 2.8%
Gas: searches of globular clusters mostly find only upper limits (Pancino et al. 2024, arXiv:2404.05548). Hubble ultraviolet colours split its red giants into a first generation and later, chemically enriched ones: 36.4% ± 2.8% first generation among 488 red giants (NGC 6254; Milone et al. 2017, MNRAS 464, 3636, Table 2).
Also in it, not measured:
- Stellar remnants: white dwarfs and neutron stars
- Almost no gas or dust: not in this tally
How we know: Distance from Gaia, Hubble and earlier distances to its stars, combined: Baumgardt & Vasiliev 2021, MNRAS 505, 5957; Baumgardt globular cluster database, combined_table.txt, retrieved 2026-10-21 (NGC 6254: 5.07 +/- 0.06 kpc). True size: the apparent size times the distance (apparent size: OpenNGC (Mattia Verga, CC BY-SA 4.0), commit 4e2398a2). Mass: Baumgardt globular cluster database, combined_table.txt (NGC 6254: 189,000 ± 2,960 Suns), retrieved 2026-10-21; Baumgardt & Vasiliev 2021, MNRAS 505, 5957.
More deep-sky objects: M12 (Globular Cluster) · M14 (Globular Cluster) · M107 (Globular Cluster) · M9 (Globular Cluster) · IC 4665 (Open Cluster) · M23 (Open Cluster)