Galaxy in Leo
M105
One of the best-measured black holes anywhere sits at the centre of this one — around 200 million solar masses — and it is measured that well because the galaxy is close enough for individual stars to be watched going round it.
That is the value of proximity: at thirty-two million light-years the motions of individual stars near the centre can be tracked, and a mass measured from orbits rather than inferred from brightness. It sits in the same low-power field as M95 and M96, which makes the Leo I group one of the easier galaxy groups to take in at once.
- Catalogue
- M105
- Type
- Galaxy
- Constellation
- Leo
- Distance
- 32 million light-years
- Apparent magnitude
- 9.3
- Surface brightness
- 21.2 mag/□″
- Apparent size
- 5′ × 4′
- Right ascension
- 10h 48m
- Declination
- +12.58°
- Found by
- Pierre Méchain, 1781
Small enough that its 9.3 magnitudes arrive concentrated rather than smeared: 21.2 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 | No | Challenge | Challenge | Challenge |
| Bortle 7 18.6 mag/□″ | No | No | 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
Small, round, bright and completely smooth, and it shares a field with two other galaxies, NGC 3384 and NGC 3389 — three in one eyepiece, of which the third is markedly fainter. The trio is the reason to come; M105 alone is a plain glow.
When, and from where
Highest in the middle of the night in March. Passes overhead at 13°N and rises from everywhere except the far south — below 77°S it never clears the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 43° | |
| 51°N London, Calgary | 52° | |
| 40°N New York, Madrid | 63° | |
| 30°N Cairo, Houston | 73° | |
| 0°N the equator | 77° | |
| 33°S Sydney, Cape Town | 44° |
Nearby in the sky
The whole catalogue →2 more of the catalogue sit within five degrees, close enough to take in on the same night without moving far. Everything below is measured from M105 itself, not from the middle of Leo.
- M96 Galaxy 48′ apart Leo · magnitude 9.2 · binoculars from Bortle 5 or darker
- M95 Galaxy 1.3° apart Leo · magnitude 9.7 · binoculars from Bortle 4 or darker
- M65 Galaxy 7.6° apart Leo · magnitude 9.3 · binoculars from Bortle 5 or darker
- M66 Galaxy 7.9° apart Leo · magnitude 8.9 · binoculars from Bortle 6 or darker
One of 110. Positions J2000; the sky is the final authority.