M30 (Globular Cluster)
A globular cluster in Capricornus, one of the most metal-poor known. Its stars formed from gas that held very few heavy elements, so they date from early in the Milky Way's history.
Globular cluster in Capricornus. Magnitude 7.4.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 60° above the southern horizon at its highest; from Lethem (3.4° N), to 64° above the southern horizon. It is highest at midnight on the night of 14 Aug, 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 7.2° south of Deneb Algedi.
- 10x50 binoculars: A round glow, brighter towards the middle.
- A small telescope (80 to 100 mm): A bright glow with a dense middle; at higher power chains of stars run out from the core.
- 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′, 29% of the Moon's width (the Moon is about 31′ wide).
- Brightness: magnitude 7.4. Fainter than the faintest stars in Georgetown (4.3) and Lethem (6.0): binoculars or a telescope.
- Distance: 27,600 light-years. The light reaching your eye left it about 27,600 years ago.
- True size: 72 light-years across its catalogued outline; light crosses it in 72 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Globular cluster
- Mass
- About 121,000 times the Sun's mass
- Notable
- One of the most metal-poor globulars: [Fe/H] -2.27, poorer than all but 2 of the 152 measured.
Measured: Which generation its red giants belong to (323 measured near its centre).
- Second generation: 62%, born from gas the first stars enriched
- First generation: 38%, ± 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: 38.0% ± 2.8% first generation among 323 red giants (NGC 7099; 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 7099: 8.46 +/- 0.09 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 7099: 121,000 ± 2,620 Suns), retrieved 2026-10-21; Baumgardt & Vasiliev 2021, MNRAS 505, 5957.
More deep-sky objects: M72 (Globular Cluster) · M75 (Globular Cluster) · M2 (Globular Cluster) · M55 (Globular Cluster) · Globular Cluster M15 · M54 (Globular Cluster)