Coma Berenices
What is Coma Berenices?
Constellations· Spring evenings (N) · star haze between Leo's tail and Arcturus. The hair Queen Berenice of Egypt offered for her husband's safe return. Instead of bright stars, its face is the Coma Star Cluster, a soft haze to the naked eye, and beyond it telescopes see thousands of distant galaxies.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Beta Comae Berenices | 4.3 |
| Diadem | 4.3 |
| Gamma Comae Berenices | 4.4 |
The 3 brightest of the 3 stars used in the figure (2 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | spring evenings (N) |
|---|---|
| Brightest star | Beta Comae Berenices (4.3) |
| How to find | the faint star swarm between Denebola and Arcturus |
| Area rank | 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The cluster where dark matter was first inferred, in 1933
About 320 million light-years away in the direction of Coma Berenices lies the Coma Cluster, a gathering of more than a thousand galaxies. In 1933 the astronomer Fritz Zwicky measured how fast the galaxies inside it were moving, and found them moving too fast. The weight of the stars we can see was not enough to hold such speedy galaxies together.
Like riders flung off a spinning fairground ride, the galaxies should have scattered. Since they had not, there had to be far more unseen mass. Zwicky called it dark matter, a term still in use. His numbers were inflated by errors in the distance measurements of his day, but he was pointing in the right direction.
The idea gained new strength about forty years later, when astronomers measured how fast galaxies rotate. It is now known that most of a galaxy cluster's mass is dark matter, the next largest share is hot gas glowing in X-rays, and stars make up only a few percent. Behind the faint star cluster of spring evenings lies the place where the idea that most of the universe is invisible first arose.
The constellation in depth
Coma Berenices is one of the few constellations tied to a person who really lived. In the 3rd century BC, Queen Berenice II of Egypt cut off her hair and offered it at a temple, as she had promised, when her husband Ptolemy III came home safely from war. When the hair vanished the next day, the court astronomer Conon pointed to this group of stars and declared that the gods had placed it in the sky.
At the centre, the Coma Star Cluster is a nearby group of stars about 280 light-years away. To the naked eye it is a faint patch; binoculars split it into dozens of stars. This direction points straight out of the disk of our galaxy, toward the galactic north pole. With few stars and little dust in the way, it is like an open window onto the distant universe.
That is why the constellation is full of galaxies. The Black Eye Galaxy, M64, has a dark band of dust beside its bright centre, like a bruised eye. At the heart of the Coma Cluster of galaxies, about 300 million light-years away, sits the giant galaxy NGC 4889, whose central black hole has been measured at about 21 billion times the Sun's mass. The globular cluster M53 is here too.
On April to June evenings, look about halfway between Denebola, the tail of Leo, and Arcturus in Boötes. Under a dark sky a faint smudge of stars appears; in town you will need binoculars. Turn on deep-sky objects in the Sky view to find NGC 4889.
Frequently asked
- When can I see Coma Berenices?
- Coma Berenices is best seen in spring evenings (N).
- How do I find Coma Berenices?
- To find Coma Berenices, look for the faint star swarm between Denebola and Arcturus.
- What is the brightest star in Coma Berenices?
- The brightest star in Coma Berenices is Beta Comae Berenices, at magnitude 4.3.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.