- M 7 (NGC 6475)
This mosaiced image of M 7 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 90-second exposures. This mosaicing was necessay because M 7 is large (1.3 degrees) and a single image acquired using the SOCO system wouldn't include the outlying stars of the cluster. The field contained in this mosaic is approximately 2 degrees across.
M 7 lies in the Milky Way stream approximately 5 degrees east of the stinger of Scorpius. With a visual magnitude of 3.3, it is easily visible to the naked eye as a fuzzy patch against the background of the Milky Way. M 7 is best observed in binoculars or a small telescope, where around 30 bright stars are revealed. The total number of stars in the cluster is around 750. While most of the bright stars in the cluster are blue-white giants, the brightest member (HD 162587) is a magnitude 5.6 yellow giant of spectral class G8 located on the lower right side of the main group in my image. M 7 is relatively close, at a distance of around 980 LY. It has a physical diameter of around 23 LY— it's apparent large size in the sky is in part due to it's closeness.
M 7 has been known since antiquity. It was included as a nebulous patch by Ptolemy in his star catalog The Almagest in 130 BC. Hodierna in 1654 was the first to observe that it consisted of individual stars. It was observed by Messier in May of 1764.
There are numerous dark nebulas forming lanes around M 7— the portions immediately to the southeast of the cluster are designated B 287. The collection of many small stars near the lower left corner of my image is the open cluster Trumpler 30. The fuzzy orange-ish spot located around two-thirds of the way from M 7 to the right edge of the image is the distant globular cluster NGC 6453.
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