M23 (Open Cluster)
A large, rich open cluster in Sagittarius, about 230 million years old and 2,330 light-years away. Gaia counts over a thousand member stars in it.
Open cluster in Sagittarius. Magnitude 5.5.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 64° above the southern horizon at its highest; from Lethem (3.4° N), to 68° above the southern horizon. It is highest at midnight on the night of 18 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: Visible to the eye only from a dark site, as a hazy knot of stars; lost in city skies. It lies 9.6° north-west of Kaus Borealis.
- 10x50 binoculars: Resolves into dozens of stars.
- A small telescope (80 to 100 mm): Too big for high power: at low power, dozens of stars fill the field.
- A camera: Spans about 40% of an APS-C frame at 2,000 mm (field 0.7° × 0.4°); needs a tracking mount.
How big, how bright, how far
- Size on the sky: 16.8′, 54% of the Moon's width (the Moon is about 31′ wide).
- Brightness: magnitude 5.5. Fainter than Georgetown's faintest stars (4.3) but brighter than Lethem's (6.0).
- Distance: 2,330 light-years. The light reaching your eye left it about 2,330 years ago.
- True size: 11 light-years across its catalogued outline; light crosses it in 11 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Open cluster
- Mass
- About 4,100 times the Sun's mass, in its stars
- Age
- About 230 million years (range 140 million years to 340 million years)
- Notable
- Rich: 1,128 member stars in the Gaia DR3 cluster catalogue.
What is in it, not measured:
- Stars born together: from one cloud of gas, at one time
- Red giants: stars that have already aged and swollen
How we know: Distance from Gaia parallaxes of its stars: Hunt & Reffert 2024, A&A 686, A42 (Gaia DR3 cluster catalogue, VizieR J/A+A/686/A42), retrieved 2026-10-21: NGC 6494 713 pc; statistical 2,325-2,329 ly (16th-84th percentile); Gaia DR3 parallax zero-point systematics (about 0.02 mas) add about 1%. True size: the apparent size times the distance (apparent size: OpenNGC (Mattia Verga, CC BY-SA 4.0), commit 4e2398a2). Mass: Hunt & Reffert 2024, A&A 686, A42 (Gaia DR3 cluster catalogue, VizieR J/A+A/686/A42), retrieved 2026-10-21, NGC 6494: total 4,104 ± 256 Suns.
More deep-sky objects: M21 (Open Cluster) · M18 (Open Cluster) · Eagle Nebula (M16) · M25 (Open Cluster IC 4725) · M28 (Globular Cluster) · M9 (Globular Cluster)