Coma Berenices

by | May 1, 2023 | 0 comments


On May evenings, our planet is turned so that we are looking out the side of the Milky Way instead of looking edgewise through its arms. This orientation means that there are few star clusters and nebulae in the evening sky right now. It also means we can look beyond our galaxy to others without our view being obstructed by the Milky Way’s dust and gas.

One of the richest galaxy concentrations in the sky lies high overhead during May, in and around an obscure constellation called Coma Berenices. This constellation consists of only three stars, none of them brighter than magnitude 4. Fortunately, Coma is not too difficult to find because it lies close to several familiar constellations containing much brighter stars.

To find the stars that make up Coma Berenices, start by finding the star Denebola in Leo (discussed in last month’s column). Draw an imaginary line connecting Denebola to Arcturus, the brightest star that is currently high in the Northern Hemisphere’s evening sky. Diadem, the only named star in Coma Berenices, lies just over halfway from Denebola to Arcturus. The star Beta Com lies 10° north of Diadem, and Gamma Com lies 10° west of Beta.

Gamma Com is at the northwestern end of a wedge-shaped group of faint stars that points down toward Diadem. This large group is actually the Coma Star Cluster, one of the nearest open clusters to Earth. Because it is so close and so large, it is easily visible with the unaided eye. Binoculars will also give good views of this group.

Galaxies are the main telescopic targets in Coma Berenices, but this constellation also holds a fine globular star cluster and a colorful double star. The globular cluster, M53, lies just 1° northeast of Diadem. M53 is not as large or bright as the best summer globulars, but an 8” telescope or larger at high magnification should give good views of the cluster and resolve some of its stars.

Coma’s best double star, 24 Com, lies about 8.5° west of Diadem. It nearly creates the fourth corner of a square, with the other three corners marked by the three main stars in the figure of Coma Berenices. However, it lies just northeast (inside the square) of where it would need to be to actually form a square. This double consists of an orange primary and a blue secondary, comfortably separated by 20”. Low magnification is adequate to split 24 Com.

NGC 4565, perhaps the finest edge-on spiral galaxy in the sky, lies 3° southeast of Gamma Com, straight in the direction of Diadem. At moderately high magnifications (100–250×), this galaxy appears as a needle-like streak of dim light, about ten times as long as it is wide. With careful observation, you should be able to see the dark dust lane that splits the galaxy’s nucleus.

M64, the Black Eye Galaxy, is Coma’s brightest galaxy. M64 is not edge-on to us, but it is slightly tilted, giving it an elongated shape. A tiny curved dust lane lies just to one side of M64’s nucleus, giving the galaxy its name. This dark dust lane is much less apparent when viewed with a telescope than it is in photographs, but you should be able to see it at high magnification with an 8” or larger telescope under a dark sky. To find M64, first locate 35 Com, a faint star located straight between Diadem and Gamma Com, slightly closer to Diadem. M64 lies about 1° northeast of 35 Com.

The heaviest concentration of galaxies in Coma Berenices lies along the border between this constellation and Virgo. While none of the galaxies in this region are particularly outstanding, the sheer number of galaxies here is impressive. One of the most enjoyable ways to explore the area is simply to scan it slowly with a telescope, starting half or two-thirds of the way from Diadem to Denebola and moving southeast toward Virgo.

Coma Berenices star map

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