Globular cluster in Ophiuchus
M19
The most oblate globular known — you can count twice as many stars along its long axis as its short. The usual explanation is tidal stretching by the galactic centre, only five thousand light-years away, though in infrared the flattening looks a good deal less dramatic, which suggests dust is exaggerating it.
It lies about five thousand light-years from the galactic centre — closer than almost anything else in the catalogue — which is where the tidal explanation comes from. Whichever reading is right, it is the one globular that visibly is not a ball, and the elongation shows in a 150mm on a good night.
- Catalogue
- M19
- Type
- Globular cluster
- Constellation
- Ophiuchus
- Distance
- 28,700 light-years
- Apparent magnitude
- 6.8
- Surface brightness
- 21.6 mag/□″
- Apparent size
- 17′
- Right ascension
- 17h 03m
- Declination
- −26.27°
- Found by
- Charles Messier, 1764
Magnitude 6.8 sounds comfortable and is spread over 17′, which brings it down to 21.6 per square arcsecond — the number that actually decides whether there is anything to see. Why surface brightness is the number that matters.
Could you see it?
Straightforward with the naked eye from Bortle 2 or darker; with 10×50 binoculars from Bortle 5.
| Sky | Eye | 10×50 | 80mm | 130mm | 200mm |
|---|---|---|---|---|---|
| Bortle 1 21.9 mag/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 2 21.7 mag/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 3 21.4 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 4 20.9 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 5 20.3 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 6 19.3 mag/□″ | No | Challenge | Challenge | Challenge | Challenge |
| Bortle 7 18.6 mag/□″ | No | No | No | No | No |
| Bortle 8 18.1 mag/□″ | No | No | No | No | No |
| Bortle 9 17.8 mag/□″ | No | No | No | No | No |
At the eyepiece
The flattening is real and visible: at 150mm the cluster is plainly wider one way than the other, which almost nothing else in this catalogue does. It never gets high from northern latitudes, so what you see is a squashed shape squashed further by the atmosphere.
When, and from where
Highest in the middle of the night in June. A southern object: overhead at 26°S, and low and murky from Britain and the northern United States even at its best. North of 64°N it never rises.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 4° | Low — in the murk |
| 51°N London, Calgary | 13° | Low — in the murk |
| 40°N New York, Madrid | 24° | |
| 30°N Cairo, Houston | 34° | |
| 0°N the equator | 64° | |
| 33°S Sydney, Cape Town | 83° |
Nearby in the sky
The whole catalogue →One more of the catalogue sits within five degrees, close enough to take in on the same night without moving far. Everything below is measured from M19 itself, not from the middle of Ophiuchus.
- M62 Globular cluster 3.9° apart Ophiuchus · magnitude 6.5 · binoculars from Bortle 6 or darker
- M9 Globular cluster 8.6° apart Ophiuchus · magnitude 7.7 · binoculars from Bortle 5 or darker
- M4 Globular cluster 8.7° apart Scorpius · magnitude 5.6 · binoculars from Bortle 5 or darker
- M6 Butterfly Cluster 10° apart Scorpius · magnitude 4.2 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.