M28 (Globular Cluster)
A compact globular cluster in Sagittarius, under a degree from the star Kaus Borealis. Messier described it in 1764 as a round nebula with no star in it.
Globular cluster in Sagittarius. Magnitude 6.8.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 58° above the southern horizon at its highest; from Lethem (3.4° N), to 62° above the southern horizon. It is highest at midnight on the night of 25 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 0.9° north-west of Kaus Borealis.
- 10x50 binoculars: A round glow, brighter towards the middle.
- A small telescope (80 to 100 mm): A small, bright, round glow; at 100x and more its edge breaks into stars. M22 is 2.9° to the east.
- 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: 5.1′, 16% of the Moon's width (the Moon is about 31′ wide).
- Brightness: magnitude 6.8. Fainter than the faintest stars in Georgetown (4.3) and Lethem (6.0): binoculars or a telescope.
- Distance: 17,500 light-years. The light reaching your eye left it about 17,500 years ago.
- True size: 26 light-years across its catalogued outline; light crosses it in 26 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Globular cluster
- Mass
- About 270,000 times the Sun's mass
- Notable
- Messier catalogued it in 1764 as a "[round] nebula containing no star"; a telescope shows the stars he could not.
What is in it, not measured:
- Old stars: among the oldest in the Milky Way
- Stellar remnants: white dwarfs and neutron stars
- Almost no gas or dust
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 6626: 5.37 +/- 0.1 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 6626: 270,000 ± 17,400 Suns), retrieved 2026-10-21; Baumgardt & Vasiliev 2021, MNRAS 505, 5957.
More deep-sky objects: Globular Cluster M22 · M21 (Open Cluster) · M25 (Open Cluster IC 4725) · M69 (Globular Cluster) · M18 (Open Cluster) · M70 (Globular Cluster)