Coma Berenices

“...curious twinkling, as if gossamers spangled with dewdrops were entangled there. One might think the old woman of the nursery rhyme who went to sweep the cobwebs out of the sky had skipped this corner, or else that its delicate beauty had preserved it even from her housewifely instinct...”

G.P.Serviss on the Coma Berenices Star Cluster.

Originally part of the tail of Leo the Lion, known as Al Halbah the ‘Tuft’, Tycho Brahe separated it from Leo in 1602, calling it Coma Berenices ‘Berenices Hair’. Legend has it that Berenice, the wife of the Egyptian king Ptolemy III, vowed to cut off her beautiful hair as a sacrifice to the goddess Aphrodite if her husband was returned safely to her. After waging war on the Assyrians, Ptolemy returned in one piece and Berenice’s hair was placed within the temple at Zephyrium.

One night, these tresses disappeared, outraging the royal pair and condemning the temple guards to execution if the hair was not returned. It was the Greek astronomer Conon of Samos who saved the day, declaring that Aphrodite was pleased with the sacrifice and had taken the hair and placed it in the sky. There it could be admired by all for eternity.

Coma Berenices is a smallish constellation of 386 sq°. Lying to the west of the bright, orange giant star Arcturus, it is surrounded by the starfields of Leo, Canes Venatici, Bootes and Virgo. The majority of the brighter stars are of the 4th and 5th magnitude.

Alpha is of magnitude 4.32, second in brightness to beta, and consisting of two F-type main sequence stars of similar size and brightness. Lying at a distance of 63 light years, alpha’s stars are about 3 times as luminous as our Sun. The mean separation of this pair is around 10 AU, about the same separation as Saturn and our Sun, completing their orbits in 25.87 years. A visual companion of magnitude 10.2 lies 89” away in position angle (PA) 345°.

Beta is a main sequence yellow dwarf star with a magnitude of 4.26. Located 29.78 light years away, beta is a near twin of our Sun, having a mass of 1.15, a radius of 1.1 and a luminosity of 1.35 Suns though slightly younger at 3 billion years of age.

A double star worth noting is 24 Comae (Struve 1657), a magnitude 5.2 orange star and a magnitude 6.7 blue star in superb contrast separated by 20.3” in PA 271° (oriented east-west). Some observers describe the 7th magnitude star’s colour as emerald, a result of it’s contrast with the orange primary.

As we look out to Coma Berenices, we look away from the Galactic Plane, leaving behind the clusters and gas and dust that crowd the spiral arms. Therefore we see more galaxies, unhindered by the obscuring material of the Milky Way.

However, there is one open cluster that could easily be overlooked. Melotte 111 is a huge group of 5th magnitude and fainter stars, just visible to the naked eye under darker skies and appearing to cover 5º of the sky. That is 10x the size of the Full Moon. Melotte 111 is one of the nearest open clusters to Earth at 250 light years. Known as the Coma Berenices Star Cluster, it contains around 50 blue-white to yellow main sequence stars of spectral types A to G. The brightest members have a luminosity around 50x that of our Sun while the faintest are of only one third the brightness of our Sun. Many of the brighter stars are evolving toward the giant stage. There are also many double and multiple systems here. The triple star 12 Comae is the brightest star with a combined magnitude of 4.83. The two companions are of magnitude 8.5 and 11.5.

Star #17 is a wide double of 145” separation, the magnitudes 5.4 and 6.7. The fainter star also has a companion of magnitude 13.7 but at 2” separation, it needs superb conditions to resolve.

NGC 4494 is a small faint elliptical galaxy appearing to lie amongst the stars of this cluster. It shows as an out of focus star so use high power to see it well.

The best galaxy in Coma Berenices and one of the best in the sky is NGC 4565. Less than 2º east of #17 Comae, this superb 10th magnitude Sb-type galaxy spans 15’ x 1.1’. It is the largest of the edge-on spirals and easily seen in small telescopes. Larger telescopes will show a long needle of light with a long dark lane running across it and a bright nuclear region north of this dust lane. At a computed distance of 30 million light years, the total luminosity is around 3 billion Suns.

Lying in the same low power field as gamma Comae is NGC 4448, an 11.4 magnitude Sb -type spiral galaxy. Use high power to put gamma out of the field to view this oval glow.

NGC 4559 lies to the east of gamma, a large Sc spiral galaxy measuring 11’ x 4’.5. It shows as an evenly lit glow with a slightly brighter central region and there are three stars superimposed upon it.

NGC 4725 lies 2º south of 31 Comae, a large barred spiral galaxy with a bright nuclear region and a surrounding mottled glow. Dark skies and a large telescope may show detail across the disk including spiral structure. Also in the same low power field are NGC 4712, an oval shaped spiral and NGC 4747, an edge on dusty spiral.

In the northeast quadrant of Coma Berenices is a remarkable field of faint galaxies. This is the Coma Berenices Galaxy Cluster, also catalogued as Abell 1656. The two brightest galaxies in this group are NGC 4874 and NGC 4889. Both of these giant systems are surrounded by a cloud of fainter galaxies, 18 around the elliptical NGC 4874 and 13 around the spiral NGC 4889. Dark skies and telescopes of 16” and larger will give views that will astound.

Around 1º east northeast of 35 Comae is M64, a large spiral galaxy discovered by J. Bode in 1779. With a luminosity of around 13 billion solar masses and a size of 44 million light years, M64 or the “Black Eye Galaxy”, to give its common name, has an unusual feature to its makeup. A large dark mass of dust outlines the northern and eastern parts of the nucleus. Photographs show much detail in this dust lane but it is more of a test in a telescope. Northern Hemisphere observers see it, under optimum conditions, with a 6” or 8” aperture. What is the smallest telescope that will show this detail within M64 from the south?

Moving on down to 11 Comae, move northeast to M85, a hybrid galaxy that combines features of an elliptical and a spiral galaxy. An outlying member of the Virgo Galaxy Cluster, it was discovered by Mechain in 1781. M85 has a mass of 100 billion Suns and lies around 44 million light years away. To the eye, it is bright and round, growing brighter toward the centre with a brighter nucleus.

NGC 4394 lies in the same field as M85, 8’ to the east. It is a small SB-type galaxy, elliptical in shape and needing high power and a largish aperture to show any detail.

Near the southern border with Virgo lies the bright 5th magnitude star 6 Comae. To the west is M98, found by Mechain in 1781. This extra-galactic wanderer is an almost edge-on spiral, much extended and bright with a brighter nucleus. M98 packs 130 billion solar masses into its 80,000 light year diameter.

M99 is a bright round Sc spiral almost 1º southeast of 6 Comae. Another of Mechain’s discoveries in 1781, it was the second galaxy to show spiral structure in Lord Rosse’s large telescope. This face-on spiral has a diameter in the region of 50,000 light years and a mass of some 50 billion solar masses. Visually, M99 is large with a bright central area and a careful observer may spot brightness variations in the disk. A large telescope will show the two spiral arms.

To the northeast of 6 Comae lies M100, the largest spiral member of the group that makes up the Virgo-Coma Galaxy Cluster. Once again discovered by Mechain, this seems to be the first galaxy detected by Lord Rosse to show spiral structure. The total luminosity is around 20 billion times our Sun and the computed mass is 160 billion solar masses. At a distance of 40 million light years, this gives a diameter of 110,000 light years, comparable to our own Milky Way. In a telescope, M100 is large and round with a brighter central area and an almost stellar nucleus.

Moving away from galaxies to something that gives a greater visual treat, swoop across to alpha Comae. Lying 1º to the northeast is the globular cluster M53. First seen by J. Bode in 1775, this bright ball of suns is easily seen in small telescopes as a small hazy spot. A larger aperture will transform this glow into myriads of stars, a beautiful cluster some 65,000 light years distant.

In the largest of telescopes, M53 is truly wonderful. Even the great Sir William Herschel was moved to remark:

“...one of the most beautiful sights I remember to have seen in the heavens. The cluster appears under the form of a solid ball consisting of small stars quite compressed into a blaze of light with a great number of loose ones surrounding it and distinctly visible in the general mass”.

Southeast of M53 by 1º is the unusual faint cluster NGC 5053. Catalogued as a globular cluster, an observer could be forgiven in thinking of it as an open cluster. Discovered by Sir William Herschel in 1784, the faint member stars are widely scattered and resolution is difficult with anything but a large telescope. NGC 5053 is thought to lie around 55,000 light years distant which gives it a luminosity of 16,000 Suns, very low for an average type globular.

This completes our brief tour of Coma Berenices, having looked at some of the more interesting objects suitable for the telescope. There are many more galaxies within this constellation’s realms, waiting to be swept up by a willing eye. Remember, most of these objects need a dark sky though a few of the brighter ones can be seen in city skies with care.

Clear skies and good hunting

~CosMos