M18 (Open Cluster)
A small, sparse open cluster in Sagittarius, about 30 million years old, between the Omega Nebula and the Small Sagittarius Star Cloud. It is easy to pass over in so rich a part of the sky.
Open cluster in Sagittarius. Magnitude 6.9.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 66° above the southern horizon at its highest; from Lethem (3.4° N), to 70° above the southern horizon. It is highest at midnight on the night of 24 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 8.5° north of Kaus Borealis.
- 10x50 binoculars: A small hazy knot with a few stars resolved. M17 is 0.9° to the north.
- A small telescope (80 to 100 mm): A loose handful of stars at low power; M17, the Omega Nebula, is 0.9° to the north.
- 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: 6′, 19% of the Moon's width (the Moon is about 31′ wide).
- Brightness: magnitude 6.9. Fainter than the faintest stars in Georgetown (4.3) and Lethem (6.0): binoculars or a telescope.
- Distance: 4,900 light-years. The light reaching your eye left it about 4,900 years ago.
- True size: 8.5 light-years across its catalogued outline; light crosses it in 8.5 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Open cluster
- Mass
- About 900 times the Sun's mass, in its stars
- Age
- About 30 million years (range 20 million years to 44 million years)
What is in it, not measured:
- Stars born together: from one cloud of gas, at one time
- Hot blue stars: still shining, because the cluster is young
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 6613 1,501 pc; statistical 4,878-4,911 ly (16th-84th percentile); Gaia DR3 parallax zero-point systematics (about 0.02 mas) add about 3%. 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 6613: total 900 ± 127 Suns.
More deep-sky objects: Eagle Nebula (M16) · M25 (Open Cluster IC 4725) · M23 (Open Cluster) · M21 (Open Cluster) · M28 (Globular Cluster) · Globular Cluster M22