Galaxy in Coma Berenices
M100
The galaxy that pinned down how fast the universe is expanding: in 1994 the newly repaired Hubble telescope picked out Cepheid variables in it, one of the first results from the programme built to settle the Hubble constant.
The result that came out of it — around eighty kilometres a second per megaparsec, with error bars that have since narrowed and moved — was the first serious measurement of the expansion rate made with individual stars in a distant galaxy. The Hubble tension that dominates cosmology now is an argument about the descendants of that number.
- Catalogue
- M100
- Type
- Galaxy
- Constellation
- Coma Berenices
- Distance
- 55 million light-years
- Apparent magnitude
- 9.3
- Surface brightness
- 22.0 mag/□″
- Apparent size
- 7′ × 6′
- Right ascension
- 12h 23m
- Declination
- +15.82°
- Found by
- Pierre Méchain, 1781
Small enough that its 9.3 magnitudes arrive concentrated rather than smeared: 22.0 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 4.
| 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 | Challenge | Challenge | Challenge | Challenge |
| Bortle 6 19.3 mag/□″ | No | No | 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
Among the larger Virgo spirals and among the fainter-looking, because face-on light is spread light. A round glow with a brighter middle at 150mm; some mottling at 250mm from a dark sky. Historically enormous, visually modest.
When, and from where
Highest in the middle of the night in March. Passes overhead at 16°N and rises from everywhere except the far south — below 74°S it never clears the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 46° | |
| 51°N London, Calgary | 55° | |
| 40°N New York, Madrid | 66° | |
| 30°N Cairo, Houston | 76° | |
| 0°N the equator | 74° | |
| 33°S Sydney, Cape Town | 41° |
Nearby in the sky
The whole catalogue →This is a busy patch. 4 more of the catalogue sit within five degrees, which is a binocular field or two — worth planning a session around rather than visiting once. Everything below is measured from M100 itself, not from the middle of Coma Berenices.
- M99 Galaxy 1.7° apart Coma Berenices · magnitude 9.9 · binoculars from Bortle 4 or darker
- M98 Galaxy 2.4° apart Coma Berenices · magnitude 10.1 · binoculars from Bortle 4 or darker
- M85 Galaxy 2.4° apart Coma Berenices · magnitude 9.1 · binoculars from Bortle 5 or darker
- M88 Galaxy 2.6° apart Coma Berenices · magnitude 9.6 · binoculars from Bortle 5 or darker
Terms on this page
- Hubble tension Two good measurements of the universe's expansion rate that stubbornly disagree.
One of 110. Positions J2000; the sky is the final authority.