Galaxy in Canes Venatici
Whirlpool Galaxy (M51)
The first object in which anybody saw spiral structure — Lord Rosse drew it in 1845 through a seventy-two-inch telescope, decades before anyone knew what a galaxy was. The small companion at the end of one arm is passing through, and the arms are the wreckage.
Rosse's drawing was made without any theory to hang it on — the word galaxy in its present sense was eighty years away — and he simply recorded a spiral because that is what he saw. NGC 5195 is on its second pass, and the arms are as clean as they are because the encounter is compressing the gas as it goes.
- Catalogue
- M51
- Type
- Galaxy
- Constellation
- Canes Venatici
- Distance
- 31 million light-years
- Apparent magnitude
- 8.4
- Surface brightness
- 21.7 mag/□″
- Apparent size
- 11′ × 7′
- Right ascension
- 13h 30m
- Declination
- +47.20°
- Found by
- Charles Messier, 1773
Small enough that its 8.4 magnitudes arrive concentrated rather than smeared: 21.7 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 | 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
The most rewarding galaxy on this list for anyone with a dark sky and 200mm, because the spiral arms are genuinely visible — not inferred, visible — along with the bridge of material reaching to the companion. From a poor sky it is two grey blobs and nothing more, and the difference is entirely the sky.
When, and from where
Highest in the middle of the night in April. Well placed for the northern hemisphere and overhead for anyone near 47°N. South of 43°S it stays below the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 77° | Never sets |
| 51°N London, Calgary | 86° | Never sets |
| 40°N New York, Madrid | 83° | |
| 30°N Cairo, Houston | 73° | |
| 0°N the equator | 43° | |
| 33°S Sydney, Cape Town | 10° | Low — in the murk |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 5.7° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M51 itself, not from the middle of Canes Venatici.
- M63 Sunflower Galaxy 5.7° apart Canes Venatici · magnitude 8.6 · binoculars from Bortle 5 or darker
- M101 Pinwheel Galaxy 8.9° apart Ursa Major · magnitude 7.9 · needs more than binoculars
- M94 Cat's Eye Galaxy 9.3° apart Canes Venatici · magnitude 8.2 · binoculars from Bortle 5 or darker
- M106 Galaxy 12° apart Canes Venatici · magnitude 8.4 · binoculars from Bortle 4 or darker
One of 110. Positions J2000; the sky is the final authority.