Globular cluster in Canes Venatici
M3
The first object Messier found himself rather than borrowed from somebody else's list, and the one that turned the catalogue from a tidying exercise into a search. It holds around half a million stars.
It also holds more variable stars than any other cluster known — around two hundred and seventy of them, nearly all RR Lyrae, whose periods give their true brightness and therefore the distance. A cluster that is not only old but that tells you how far away it is.
- Catalogue
- M3
- Type
- Globular cluster
- Constellation
- Canes Venatici
- Distance
- 34,000 light-years
- Apparent magnitude
- 6.2
- Surface brightness
- 21.1 mag/□″
- Apparent size
- 18′
- Right ascension
- 13h 42m
- Declination
- +28.38°
- Found by
- Charles Messier, 1764
Magnitude 6.2 sounds comfortable and is spread over 18′, which brings it down to 21.1 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 3 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/□″ | Easy | 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
One of the few globulars that rewards pushing the magnification hard. It resolves from the outside in, so the first stars appear around the rim while the core stays a solid glow — and on a steady night at 200x that core keeps breaking down further the longer you look at it.
When, and from where
Highest in the middle of the night in April. Passes overhead at 28°N and rises from everywhere except the far south — below 62°S it never clears the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 58° | |
| 51°N London, Calgary | 67° | |
| 40°N New York, Madrid | 78° | |
| 30°N Cairo, Houston | 88° | |
| 0°N the equator | 62° | |
| 33°S Sydney, Cape Town | 29° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 12° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M3 itself, not from the middle of Canes Venatici.
- M53 Globular cluster 12° apart Coma Berenices · magnitude 7.6 · binoculars from Bortle 5 or darker
- M64 Black Eye Galaxy 12° apart Coma Berenices · magnitude 8.5 · binoculars from Bortle 5 or darker
- M63 Sunflower Galaxy 15° apart Canes Venatici · magnitude 8.6 · binoculars from Bortle 5 or darker
- M94 Cat's Eye Galaxy 16° apart Canes Venatici · magnitude 8.2 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.