M 4 Deep sky · Globular cluster in Scorpius · M 4 · NGC 6121
Crab Globular Cluster
A globular cluster right beside Antares — one of the closest to the Sun, and loose enough that a small telescope shows a bar of stars across its middle.
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- Type
- Globular cluster
- Designations
- M 4 · NGC 6121
- Constellation
- Scorpius
- Apparent magnitude
- 5.9
- Apparent size
- 26′
- Position (J2000)
- RA 16h 24m · Dec −26° 32′
It is about as wide as the full Moon, which is about 31′ across. The Sun passes 5° from it around late November, and for about 28 days of the year it sits within 15° of the Sun, lost in its glare.
When to see it
On the night of Tue 25 May 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 21:48 | 01:12 · 12° | 04:35 |
| New York EDT | 20:49 | 01:07 · 23° | 05:24 |
| Singapore GMT+8 | 19:21 | 01:17 · 62° | 07:14 |
| Sydney GMT+10 | 16:51 | 00:08 · 83° | 07:26 |
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 May, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by late August it is highest in the early evening, and in late February not until the hours before dawn.
- How bright is it?
- Magnitude 5.9 in total, but that light is spread over 26′ of sky: on average 21.6 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?
- The naked eye, from a dark country sky, which shows stars to about magnitude 7.0; from a city, binoculars.
Look for
Put Antares in the binoculars and look just to its west: a round, soft glow that the star’s glare can hide on a hazy night.
Science
Hubble found some of the oldest white dwarfs known in it, and a pulsar in it has a planet — one of the oldest planets yet found.
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 5.9 against the faintest star each can show: the eye under a city sky, 4.5 (1.4 short); the eye under a dark country sky, 7.0 (1.1 to spare); 50 mm binoculars under that dark sky, 11.0 (5.1 to spare); a 100 mm telescope there, 12.5 (6.6 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 6% of the field’s width; through a 100 mm telescope at 50×, a field about 1° across, it spans 43% of the field’s width.