Globular cluster in Ophiuchus
M9
There is a wall of dust between us and this one, thick enough to steal about a magnitude off it. Take that away and M9 would be a comfortable binocular target rather than the marginal smudge it actually is.
It lies only about five and a half thousand light-years from the centre of the galaxy, which is close enough that its outer stars are being pulled away. The dust responsible for dimming it is Barnard 64, a dark nebula lying almost against its western edge — visible as an absence, if the sky is good enough to show what it is subtracting.
- Catalogue
- M9
- Type
- Globular cluster
- Constellation
- Ophiuchus
- Distance
- 25,800 light-years
- Apparent magnitude
- 7.7
- Surface brightness
- 21.7 mag/□″
- Apparent size
- 12′
- Right ascension
- 17h 19m
- Declination
- −18.52°
- Found by
- Charles Messier, 1764
Magnitude 7.7 sounds comfortable and is spread over 12′, which brings it down to 21.7 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 1 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/□″ | No | 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
Small, dim and unhelpfully placed against a busy field. At 150mm it stays granular rather than resolving, and the dust in front takes the edge off everything. A useful demonstration that a globular's catalogue magnitude tells you very little about how it will actually look.
When, and from where
Highest in the middle of the night in June. Overhead at 19°S and southerly enough to sit low from northern Europe, though never out of reach there — only north of 71°N does it stop rising at all.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 11° | Low — in the murk |
| 51°N London, Calgary | 20° | |
| 40°N New York, Madrid | 31° | |
| 30°N Cairo, Houston | 41° | |
| 0°N the equator | 71° | |
| 33°S Sydney, Cape Town | 76° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 8.6° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M9 itself, not from the middle of Ophiuchus.
- M19 Globular cluster 8.6° apart Ophiuchus · magnitude 6.8 · binoculars from Bortle 5 or darker
- M23 Open cluster 8.9° apart Sagittarius · magnitude 5.5 · binoculars from Bortle 9 or darker
- M20 Trifid Nebula 11° apart Sagittarius · magnitude 6.3 · binoculars from Bortle 3 or darker
- M21 Open cluster 11° apart Sagittarius · magnitude 6.5 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.