Let’s you and I slip into an astronomical Coma

With a little help from Alkaid, the star at the end of the Big Dipper's Handle, and bright Mars and Arcturus, you can snare the Coma cluster within a large triangle. This photo shows the sky facing east around 10:30 p.m. Arcturus and Mars are separated by about five fists held at arm's length. Photo: Bob King

Walking around in a coma is easy for amateur astronomers. Successive clear nights combined with a determination to see everything within your telescope’s reach before the next cloudy spell is a sure ticket to zombiehood. I know. I’ve been there.

Queen Berenice's tresses are forever in the sky between the Big Dipper and Leo. Credit: Urania's Mirror

But that’s not the coma we’ll touch on today. This Coma is short for Coma Berenices or Bernice’s Hair. It’s one of the few constellations that represents a real person, Queen Berenice of Egypt born in about 266 B.C. When her husband, Ptolemy III, went off to war, the Queen vowed to cut off her hair in gratitude to the gods if he returned unharmed. When he did, she carried out the vow and placed her locks in a temple dedicated to Aphrodite. When the hair was discovered missing the next day, astronomer and mathematician Conon of Samos explained to the king that it had been whisked away to the heavens as the fuzzy cluster of stars in the tail of Leo the Lion.

This map shows both the Coma star cluster and the Coma galaxy cluster (described below). Both are located in the "tail end" of Leo the Lion east or left of Mars. Three stars outline a simple triangle that forms the constellation Coma Berenices. Created with Stellarium

No adult would believe such as story today, but what 21st century king or president would turn down the opportunity for immortality in the sky? Today we know that Berenice’s hair is a nearby star cluster 180 light years from Earth or 2 1/2 times closer than the familiar Pleiades or Seven Sisters cluster. The Coma cluster contains about 40 stars spread across 4.5 degrees. That means it completely fills the field of view of a typical pair of binoculars.

Not that you need binoculars. In a light-polluted sky, Coma fades into the background, but from outer ring suburbs, and especially the country, it’s a delightful starry mist high in the eastern sky around 10  o’clock.

The Coma galaxy cluster, one of the densest concentrations of galaxies in the sky, is a spherical cluster some 20 million light years wide. Click photo to enlarge. Credit: NASA/ESA

Little did the king or queen of Egypt know that there was more treasure in those tresses than meets the naked eye.  Stashed away inside the little blue circle on the map above are over 1,000 galaxies, all member of the Coma galaxy cluster. It’s one of the richest in the sky and contains lots of old, star-packed elliptical galaxies along with a sprinkling of spirals like our Milky Way.

Most are 12th magnitude or fainter, because the cluster is more than 300 million light years away. You might see a dozen of these galactic “fuzzballs” in an 8-inch scope. A 15 or 16 incher will show many more. I spent a rewarding night with the cluster a few years back. Armed with a good map , I tracked down at least two dozen galaxies in the core alone, every one of which fit into a single field of view. The impression was of flowers in field.

Astronomer Fritz Zwicky, the first to suggest "dark matter" in space. Credit: zwicky.stiftung.ch

Back in the 1930s Swiss-American astronomer Fritz Zwicky estimated the mass of the Coma cluster and then observed the motion of its many galaxies. It turned out that the galaxies were moving much too fast to remain in the cluster. Something else – invisible to any telescope and very massive – had to keep them from flying apart. He called it “dunkle Materie” or dark matter.

Coma was our first introduction to this strange stuff. We still don’t know what it is except that its gravity can tug on things like ordinary matter. Dark matter makes up 25% of the universe, dark energy (another unknown form of energy causing the expansion of the universe to accelerate) about 70% and ordinary matter – what you and I are made of – less than 5%.  In light of those numbers, Earth and its inhabitants are a precious lot.