NGC 6397 (Globular Cluster)
The second-nearest globular cluster, in Ara, about 8,100 light-years away. It is large and bright, but from Guyana it stays below 30° in the south.
Globular cluster in Ara. Magnitude 5.5.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 30° above the southern horizon at its highest; from Lethem (3.4° N), to 33° above the southern horizon. It is highest at midnight on the night of 14 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 fuzzy star; lost in city skies. It lies 10.7° south of Sargas.
- 10x50 binoculars: A round glow, brighter towards the middle.
- A small telescope (80 to 100 mm): A large, bright glow that a small telescope resolves at the edge; low in the south from Guyana.
- 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: 15.3′, 49% 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: 8,090 light-years. The light reaching your eye left it about 8,090 years ago.
- True size: 36 light-years across its catalogued outline; light crosses it in 36 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Globular cluster
- Mass
- About 82,000 times the Sun's mass
- Notable
- The second nearest of the 167 globulars in the Baumgardt database, after M4; its core has collapsed into a very dense centre.
Measured: Which generation its red giants belong to (111 measured near its centre).
- Second generation: 65.5%, born from gas the first stars enriched
- First generation: 34.5%, ± 3.6%
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: 34.5% ± 3.6% first generation among 111 red giants (NGC 6397; 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 6397: 2.48 +/- 0.02 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 6397: 82,400 ± 1,350 Suns), retrieved 2026-10-21; Baumgardt & Vasiliev 2021, MNRAS 505, 5957.
More deep-sky objects: NGC 6388 (Globular Cluster) · NGC 6541 (Globular Cluster) · S Normae Cluster (NGC 6087) · NGC 6752 (Globular Cluster) · NGC 6231 (Northern Jewel Box) · NGC 6025 (Open Cluster)