The Virgo Galaxy Cluster

The distribution of galaxies within the Universe tends to be in clusters. The one nearest our local cluster is the Virgo Galaxy Cluster. It contains about 1500 galaxies, it is roughly circular when viewed from Earth, and its width is about 8 degrees, or about the width of 16 full moons. Like the stars in a star cluster, the galaxies in a cluster are gravitationally related to one another. Because of the cluster’s large size, and because even the brightest galaxies are quite dim, it is not observable at all with the unaided eye, and even the best telescope can see but a portion of the cluster at one time. The best way to observe the cluster is photographically in a wide field of view. Here is my attempt to photograph the cluster last year:

There are about 30 galaxies in this inverse image, and they can be identified with their Messier catalog number (e.g. M86) or their New General Catalog (NGC) number. In a good quality, properly adjusted display, each of the galaxies can be seen as a smudge inside the circle near the M or NGC labels. The source data for this image is 24 full frame, single exposures that were stacked together to reduce the noise (graininess). Each of the individual images were exposed for 30 seconds at f/5.6, ISO 800 using a 70mm lens. Although my camera was guided, an unguided exposure of field this wide should have only very minor star trails, which are caused by the Earth’s rotation during the 30 seconds that the camera shutter was open. The galaxies could be brighter, and perhaps more of them could be seen if a lower f/ number or a higher ISO were used. Experiment with various camera settings, and consult a star chart on line to determine where to point the camera.

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