M 68 Deep sky · Globular cluster in Hydra · M 68 · NGC 4590
M 68
A globular cluster in Hydra, just below the crow of Corvus — one of the few that light the spring sky.
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- Type
- Globular cluster
- Designations
- M 68 · NGC 4590
- Constellation
- Hydra
- Apparent magnitude
- 7.3
- Apparent size
- 11′
- Position (J2000)
- RA 12h 39m · Dec −26° 45′
The full Moon, about 31′ across, is 2.8 times as wide. The Sun comes no nearer to it than 21°, around mid October, so it is never lost in the Sun’s glare, which reaches about 15° out.
When to see it
On the night of Tue 30 Mar 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 21:47 | 01:08 · 12° | 04:29 |
| New York EDT | 20:47 | 01:03 · 22° | 05:19 |
| Singapore GMT+8 | 19:17 | 01:14 · 62° | 07:10 |
| Sydney GMT+11 | 17:46 | 01:05 · 83° | 08:23 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 13° up in the south.
- Can I see it from 35° south?
- Yes, and well placed: at its highest it passes almost overhead, 82° up, above most of the air’s haze.
- When is the best time of year to see it?
- Around late March, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by late June it is highest in the early evening, and in late December not until the hours before dawn.
- How bright is it?
- Magnitude 7.3 in total, but that light is spread over 11′ of sky: on average 21.1 magnitudes per square arcsecond. Against a dark country sky that average stands out; a city’s glow drowns all but its brightest parts.
- Naked eye, binoculars or telescope?
- Binoculars. At magnitude 7.3 it is past the eye, but a 50 mm pair under a dark sky reaches about magnitude 11.0.
Look for
Start from Algorab in Corvus and drop south. Binoculars show a small, faint glow; a telescope begins to resolve its edges.
Look for
From 50° north it climbs to 13°; from 35° north it climbs to 28°; from the equator it climbs to 63°; from 35° south it climbs to 82°.
Look for
Magnitude 7.3 against the faintest star each can show: the eye under a city sky, 4.5 (2.8 short); the eye under a dark country sky, 7.0 (0.3 short); 50 mm binoculars under that dark sky, 11.0 (3.7 to spare); a 100 mm telescope there, 12.5 (5.2 to spare). Those limits are for a point of light; its light is spread over its whole size, so it needs some of that margin in hand. Through 7×50 binoculars, whose field is about 7.1° across, it spans 3% of the field’s width; through a 100 mm telescope at 50×, a field about 1° across, it spans 18% of the field’s width.