NGC 6388 (Globular Cluster)
One of the most massive globular clusters in the Milky Way, in Scorpius, 1.7° from Sargas. It weighs about 1.3 million Suns, and its stars are rich in heavy elements for a globular.
Globular cluster in Scorpius. Magnitude 6.8.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 38° above the southern horizon at its highest; from Lethem (3.4° N), to 42° above the southern horizon. It is highest at midnight on the night of 13 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 1.7° south of Sargas.
- 10x50 binoculars: A round glow, brighter towards the middle.
- A small telescope (80 to 100 mm): A small, bright, concentrated glow that looks like a fuzzy star at low power.
- 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: 8.4′, 27% 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: 36,400 light-years. The light reaching your eye left it about 36,400 years ago.
- True size: 89 light-years across its catalogued outline; light crosses it in 89 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Globular cluster
- Mass
- About 1.31 million times the Sun's mass
- Notable
- The fourth heaviest of the 167 globulars in the Baumgardt database, and metal-rich: [Fe/H] -0.55, richer than 130 of 152.
Measured: Which generation its red giants belong to (1,735 measured near its centre).
- Second generation: 75.5%, born from gas the first stars enriched
- First generation: 24.5%, ± 1.0%
Milone et al. class it Type II: it also holds a third, iron-enriched group of stars, so this two-way split is the simplest reading. 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: 24.5% ± 1.0% first generation among 1,735 red giants (NGC 6388; 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 6388: 11.17 +/- 0.16 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 6388: 1,310,000 ± 11,400 Suns), retrieved 2026-10-21; Baumgardt & Vasiliev 2021, MNRAS 505, 5957.
More deep-sky objects: NGC 6541 (Globular Cluster) · NGC 6231 (Northern Jewel Box) · NGC 6281 (Open Cluster) · NGC 6397 (Globular Cluster) · Ptolemy Cluster (M7) · War and Peace Nebula (NGC 6357)