Globular cluster in Sagittarius
M75
The most remote globular in the catalogue that actually belongs to our galaxy. M54 is further out, but M54 turned out not to be ours. Nearly all of M75's light comes from a core a couple of arcminutes across, and at this range it stays a fuzzy dot in almost anything.
It is unusually concentrated — one of the densest globulars in the catalogue — which is why nearly all the light is in the core and why nothing short of a large aperture will grain even the edges. At sixty-seven thousand light-years it is roughly two and a half times as far as the galactic centre.
- Catalogue
- M75
- Type
- Globular cluster
- Constellation
- Sagittarius
- Distance
- 67,500 light-years
- Apparent magnitude
- 8.5
- Surface brightness
- 21.0 mag/□″
- Apparent size
- 6′
- Right ascension
- 20h 06m
- Declination
- −21.92°
- Found by
- Pierre Méchain, 1780
Small enough that its 8.5 magnitudes arrive concentrated rather than smeared: 21.0 per square arcsecond, which is why it stands out from the sky better than its brightness alone suggests. Why surface brightness is the number that matters.
Could you see it?
Straightforward with 10×50 binoculars from Bortle 5.
| Sky | Eye | 10×50 | 80mm | 130mm | 200mm |
|---|---|---|---|---|---|
| Bortle 1 21.9 mag/□″ | No | 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
Dense, small and unresolvable, with a bright middle that no amateur aperture will break up at this distance. Its compactness is the only visible characteristic, and knowing what that compactness means is most of the interest.
When, and from where
Highest in the middle of the night in July. Overhead at 22°S and southerly enough to sit low from northern Europe, though never out of reach there — only north of 68°N does it stop rising at all.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 8° | Low — in the murk |
| 51°N London, Calgary | 17° | Low — in the murk |
| 40°N New York, Madrid | 28° | |
| 30°N Cairo, Houston | 38° | |
| 0°N the equator | 68° | |
| 33°S Sydney, Cape Town | 79° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 11° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M75 itself, not from the middle of Sagittarius.
- M55 Globular cluster 11° apart Sagittarius · magnitude 6.3 · binoculars from Bortle 5 or darker
- M72 Globular cluster 15° apart Aquarius · magnitude 9.4 · binoculars from Bortle 4 or darker
- M73 Asterism 16° apart Aquarius · magnitude 9.0 · binoculars from Bortle 6 or darker
- M54 Globular cluster 18° apart Sagittarius · magnitude 7.6 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.