Globular cluster in Capricornus
M30
Another collapsed core, with two thin chains of stars trailing away — the marks of having been dragged through the galactic disc more than once. Low in the south, and neglected mostly for that.
The core collapse means the middle is genuinely denser than a globular's centre normally gets, dense enough that stars collide and merge there — the blue stragglers, which look far too young for a cluster thirteen billion years old and are exactly that: young stars, made recently out of old ones.
- Catalogue
- M30
- Type
- Globular cluster
- Constellation
- Capricornus
- Distance
- 27,100 light-years
- Apparent magnitude
- 7.2
- Surface brightness
- 21.2 mag/□″
- Apparent size
- 12′
- Right ascension
- 21h 40m
- Declination
- −23.18°
- Found by
- Charles Messier, 1764
Magnitude 7.2 sounds comfortable and is spread over 12′, which brings it down to 21.2 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 | Challenge | Challenge | Challenge | Challenge |
| Bortle 8 18.1 mag/□″ | No | No | No | No | No |
| Bortle 9 17.8 mag/□″ | No | No | No | No | No |
At the eyepiece
The collapsed core reads as a hard bright centre with a scattering around it, and the two chains of stars running north are findable at 200mm if the seeing is steady. Low from northern latitudes, which costs it most of the detail it might otherwise give up.
When, and from where
Highest in the middle of the night in August. Overhead at 23°S and southerly enough to sit low from northern Europe, though never out of reach there — only north of 67°N does it stop rising at all.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 7° | Low — in the murk |
| 51°N London, Calgary | 16° | Low — in the murk |
| 40°N New York, Madrid | 27° | |
| 30°N Cairo, Houston | 37° | |
| 0°N the equator | 67° | |
| 33°S Sydney, Cape Town | 80° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 14° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M30 itself, not from the middle of Capricornus.
- M73 Asterism 14° apart Aquarius · magnitude 9.0 · binoculars from Bortle 6 or darker
- M72 Globular cluster 15° apart Aquarius · magnitude 9.4 · binoculars from Bortle 4 or darker
- M75 Globular cluster 22° apart Sagittarius · magnitude 8.5 · binoculars from Bortle 5 or darker
- M2 Globular cluster 22° apart Aquarius · magnitude 6.5 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.