M68 (Globular Cluster)
A globular cluster in Hydra, 3.5° from Kraz in Corvus. Its stars are very poor in heavy elements, relics of an early epoch of the galaxy.
Globular cluster in Hydra. Magnitude 8.0.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 56° above the southern horizon at its highest; from Lethem (3.4° N), to 60° above the southern horizon. It is highest at midnight on the night of 30 Mar, 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 3.5° south of Kraz.
- 10x50 binoculars: A round glow, brighter towards the middle.
- A small telescope (80 to 100 mm): A round, loose glow that a small telescope starts to resolve at its edge.
- 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: 6.6′, 21% of the Moon's width (the Moon is about 31′ wide).
- Brightness: magnitude 8.0. Fainter than the faintest stars in Georgetown (4.3) and Lethem (6.0): binoculars or a telescope.
- Distance: 33,900 light-years. The light reaching your eye left it about 33,900 years ago.
- True size: 65 light-years across its catalogued outline; light crosses it in 65 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Globular cluster
- Mass
- About 128,000 times the Sun's mass
- Notable
- Very metal-poor: [Fe/H] -2.23, poorer than all but 4 of the 152 globulars measured.
Measured: Which generation its red giants belong to (330 measured near its centre).
- Second generation: 61.9%, born from gas the first stars enriched
- First generation: 38.1%, ± 2.4%
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: 38.1% ± 2.4% first generation among 330 red giants (NGC 4590; 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 4590: 10.4 +/- 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 4590: 128,000 ± 5,950 Suns), retrieved 2026-10-21; Baumgardt & Vasiliev 2021, MNRAS 505, 5957.
More deep-sky objects: Omega Centauri (NGC 5139) · Jewel Box Cluster (NGC 4755) · Wishing Well Cluster (NGC 3532) · NGC 3603 (Nebula and Cluster) · Running Chicken Nebula (IC 2944) · NGC 3324 (Nebula and Cluster)