Globular cluster in Serpens
M5
Around thirteen billion years old, which makes it older than the disc of the galaxy it now orbits and not far off the age of the universe. Observers who compare the two honestly tend to rate it above M13, and from southern latitudes they are plainly right.
It is around 165 light-years across and holds a hundred thousand stars or more, on an orbit that carries it far out of the disc and back. Its stars are almost entirely hydrogen and helium: they condensed before any generation had lived long enough to manufacture much else.
- Catalogue
- M5
- Type
- Globular cluster
- Constellation
- Serpens
- Distance
- 25,000 light-years
- Apparent magnitude
- 5.6
- Surface brightness
- 21.0 mag/□″
- Apparent size
- 23′
- Right ascension
- 15h 19m
- Declination
- +2.08°
- Found by
- Gottfried Kirch, 1702
Magnitude 5.6 sounds comfortable and is spread over 23′, which brings it down to 21.0 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 from a Bortle 5 sky or darker, and aperture makes almost no difference to that — spread this thinly, an object is limited by how bright the sky behind it is rather than by how much light the telescope collects. A darker site beats a bigger telescope.
| 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/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 4 20.9 mag/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 5 20.3 mag/□″ | Easy | 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
Noticeably lopsided at the eyepiece — brighter and denser on one side — which is unusual enough in a globular to be worth looking for. Chains of stars curve away from the core on the eastern edge. Give it 150mm and time to dark-adapt and it competes with anything on this list.
When, and from where
Highest in the middle of the night in May. Close enough to the celestial equator to rise from almost anywhere on Earth, and to pass overhead for anyone near 2°N.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 32° | |
| 51°N London, Calgary | 41° | |
| 40°N New York, Madrid | 52° | |
| 30°N Cairo, Houston | 62° | |
| 0°N the equator | 88° | |
| 33°S Sydney, Cape Town | 55° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 23° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M5 itself, not from the middle of Serpens.
- M12 Globular cluster 23° apart Ophiuchus · magnitude 6.7 · binoculars from Bortle 5 or darker
- M107 Globular cluster 24° apart Ophiuchus · magnitude 8.1 · binoculars from Bortle 5 or darker
- M10 Globular cluster 25° apart Ophiuchus · magnitude 6.6 · binoculars from Bortle 5 or darker
- M80 Globular cluster 29° apart Scorpius · magnitude 7.3 · binoculars from Bortle 6 or darker
One of 110. Positions J2000; the sky is the final authority.