By Jim Kaler

When I was young, I would visit my cousins in southern New York State, where it was insanely dark: to outsiders' surprise, New York, home of New York City, is mostly rural and home also to mountains, farms, cows, and good cheese. Directly south of the Big Dipper's handle (in Britain, the Plough), on one trip I first saw this amazing spattering of stars that looked like lace affixed to the firmament. It was hard to look away. Coma Berenices, Berenices Hair, honors an ancient Queen who vowed to cut off her hair and offer it to Aphrodite if her husband returned safely from battle. He did, she did, and the gods put it into the sky.

As a constellation, Coma is something of a hybrid. Though honored in ancient times, Ptolemy did not include it in his list. It was later added back by Tycho when modern astronomers (1600-1800) began filling in the sky, Flamsteed making use of it in his great catalogue. Though the really modern (1930) boundaries spread out farther, the constellation's lacy core is a modest open cluster more formally called Melotte 111 (after the British astronomer P.J. Melotte). Leaving aside the Ursa Major Cluster (dominated by the middle five stars of the Dipper), with a distance of around 300 light years, twice as far as the Hyades, Mel 111 is the second closest cluster, and is just over two-thirds of the way to the Pleiades and halfway to the Beehive. Some 500 million years old, the combined gravity of its stars is not enough to keep it together. Coma is particularly known for its lack low mass stars, many of which have already departed.

Just a few degrees to the east of the cluster lies the North Galactic Pole, which stands perpendicular to the midline of the Milky Way. Looking away from our Galaxy's dusty disk gives us a wonderfully clear view of distant galaxies, which are absent from the Galactic plane, the old astronomers -- not knowing the natures of galaxies nor of interstellar dust -- referring to it as the "zone of avoidance."

Coma Berenices, the broader constellation that includes the cluster, has few other bright stars of interest. For these, look between Coma and the Dipper's handle for a pair that run parallel to the latter. Here is a real "modern" constellation, Canes Venatici, the Hunting Dogs, invented by Hevelius in the seventeenth century from the "unformed" stars of Ursa Major. The luminary, third magnitude Cor Caroli ("Charles Heart," named by Edmund Halley in honor of Charles II), 115 light years away, is a binary made of a dominant magnitude 2.90 class A0 dwarf called Alpha-2 (as it's the eastern of the two) coupled with a magnitude 5.60 F0 dwarf (Alpha-1) 19 seconds of arc away. They have been tracking each other since Herschel first measured their separation in 1777. With a weird surface composition powerfully enhanced by silicon, mercury, europium, and various other elements, Alpha-2 is the prototype of the class A magnetic stars that slop over into the B and F dwarfs. In the outer layers of slowly rotating (hence quiescent) "metallic" (Am etc.) stars, some elements are raised by radiative lofting, while gravity causes others to settle downward. In the magnetic (Ap) stars, strong fields up to tens of thousands of times that of Earth (Alpha-2 at about 2000) concentrate the enhanced elements into patches, "starspots." As a magnetic star rotates, its field axis, which is tilted against the rotation axis, flops around, and the star varies slightly in brightness as its starspots swing in and out of view, Alpha-2 going around every 5.469 days. Analysis of the Doppler shifts in the various spectrum lines allows the construction of a movie of the rotating star, spots and all. If that is not enough, Alpha-1 seems to be a metallic star.

The other star of the configuration, fourth magnitude Beta CVn (or Chara, meaning "Joy"), a mere 27.3 light years away, is a G0 dwarf a lot like the Sun. Almost the same temperature, it's 19 percent more luminous, possibly as a result of more advanced age and/or slightly higher mass. And like the Sun, it radiates X-rays from a hot corona. Alas, there seems to be no planet, perhaps the result of a notably lower metal content. Largely unsung is "La Superba," Y CVn, a red carbon star, though one not nearly so red as beautiful R Leporis, "Hind's Crimson Star." Carbon stars have molecular absorptions of cyanogen (CN) and other features that wipe out the blue parts of their spectra, leaving them as glowing coals. In an advanced state of evolution, they are brightening as giants for the second time with shrinking dead carbon/oxygen cores, and have through convection shoveled up carbon manufactured deep down by helium fusion.

Near the southern border of Canes Venatici, between Cor Caroli and Arcturus, lies one of the Galaxy's great stellar systems, the globular cluster Messier 3. Just over thirty thousand light years away, 100 times the distance of the Coma cluster, exceeded in absolute brightness by only 47 Tucanae, Omega Centauri, and perhaps M5 in Serpens, it may contain as many as a million stars. Flipping to the northern border, 3.5 degrees southeast of Alkaid (Eta Ursae Majoris) at the end of the Dipper's handle, find an even more spectacular system, M51, the Whirlpool Nebula, a classic spiral galaxy some 25 million light years away (the distance uncertain), nearly a thousand times farther than M3. In 1845, William Parsons, third Earl of Rosse, used his giant 72-inch telescope to discover the galaxy's spiral arms. Until Hubble figured out they were galaxies, M51 and a cohort of other "spiral nebulae" were commonly thought to be small and in our own large Galaxy. Rosse's spiral arm drawing was so dramatic that it showed up in van Gogh's "Starry Night." At M51's north edge is a small satellite galaxy, NGC 5195, that is tidally disrupting M 51 and is likely responsible for the beautiful spiral structure and a high star formation rate. At the center of M51 is a modest supermassive black hole similar to the one at the center of our Galaxy. M51 seems to be a gravitational partner with M63 six degrees to the south- southwest.

Up in Canes Venatici's northwest corner, the nucleus of the spiral galaxy M106 (NGC 4258) contains a water "megamaser" (a powerful natural microwave laser) from gas in orbit around an active supermassive black hole that is devouring its surroundings. The velocity of the maser from its maximum Doppler shift coupled to the motion across the line of sight yields a distance of 23.5 million light years, accurate to a couple tenths, making the galaxy a foundation stone in the cosmic distance ladder from which we derive the expansion and acceleration rates of the Universe.

With galaxies in mind, drop back to Coma Berenices. At the constellation's southern edge lies the spillover of the vast Virgo Cluster of galaxies. With a distance of around 55 million light years, it's the nearest large cluster, splashing some 15 degrees across the sky. We are closely related to it as part of the Virgo supercluster. Of its 16 Messier galaxies (the most famous the giant elliptical M87 with its relativistic jet), six fall into Coma Berenices: M84, 88, 91, 98, 99, and 100, all spirals of one sort or another. Of the six, M100 is notable for its role in the Hubble Space Telescope's Key Project to use its Cepheid variables to help establish the distance scale of the Universe.

There are enough Virgo cluster galaxies within the bounds of Coma Berenices that it is sometimes called the Virgo-Coma cluster. That can be confusing, as near the constellation's northeastern corner we find a separate Coma Berenices galaxy cluster that lies 300 million light years away, another 10 of so times farther than M51. Two huge ellipticals dominate it, NGC 4874 and 4889. In the 1930s, Fritz Zwicky measured the radial (line of sight) velocities of several of its members relative to the cluster's average recession speed. He found that the individual galaxies were orbiting within the cluster much faster than expected given the members' estimated masses, and surmised that some kind of pervasive "dark matter" must pervade the system. While part of it is hot intergalactic gas, the rest remains mysterious. The existence of the stuff is bolstered by galaxy rotation speeds (derived from such beauties as edge-on NGC 4565 in Coma), gravitational lensing, and the cosmic microwave background. Dark matter constitutes a quarter the mass- energy of the Universe and we still do not know what it is, Coma's legacy extending far beyond her beautiful hair.

Copyright © James B. Kaler, all rights reserved. These contents are the property of the author and may not be reproduced in whole or in part without the author's consent except in fair use for educational purposes. First published in the August 2014 Newsletter of the Lowestoft and Great Yarmouth Regional Astronomers, who are gratefully acknowledged.