- M 45 The Pleiades
This mosaiced image of M 45 was created from 5 images— one of the center of the cluster and the other four forming the corners around it. Each of the five images was created from 16 60-second exposures. This mosaicing was necessay because the cluster is too large (2 degrees) to be adequately captured in a single image using the SOCO system.
All the brighter stars in the cluster are young spectral class B stars. The Pleiades are quite close to us— 425 LY away. This distance is known to be fairly accurate, since the stars of the cluster are close enough to us to measure their distance by parallax. As might be expected from the spectral types of its stars, the Pleiades is very young— only around 100 million years old. It is believed that the cluster will disperse over the next 250 million years due to external gravitational forces. One of the features of the Pleiades hinted at in my image is the presence of a tenuous, wispy reflection nebula within which the star cluster lies. Most prominent is the portion around Merope (bottom star in this view of the cluster), which bears the name the Merope Nebula (NGC 1435). Also visible is the nebulosity around Maia (NGC 1432), which lies directly above Merope.
Charles Messier included the Pleiades as number 45 in his catalog of "nebulous objects" published in 1769, along with M 42 and M 43 (parts of the Orion Nebula) and M 44 (the Beehive Cluster), most likely to round up his list of objects to 45. The Pleiades have been known from antiquity, with references to them appearing in the Mesopotamian clay tablets of the Second Millenium BCE. They also may be represented on Neolithic artwork and cave paintings going back 20,000 to 30,000 years.
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