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| M7 an Open Cluster sometimes known as Ptolemy's Cluster, - this image cropped and downsized from the original photo |
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A large and bright cluster, easily seen with the unaided eye. A real beauty in a binocular view. To me the remarkable thing is the huge number of background stars. In the full frame view, I estimate there's at least 15,000 detectable stars in the little over 1/2 degree field of view. That's because it's in the middle of the Milky Way's stream, just a little to the right and below the teapot's spout. Ptolemy mentioned it about 130 AD and described it as the "nebula following the sting of Scorpius." The description may also include M6, but this is uncertain. Because of this presumable discovery, the name "Ptolemy's Cluster" for M7 was proposed some years ago, a proposition which has found some acceptance. M7 consists of about 80 stars brighter than magnitude 10 in a field of about 1.3 degrees apparent diameter which at its distance of perhaps 800 light years corresponds to a linear extension of 18 or 20 light years. This group is approaching us at 14 km/sec. M7's age was estimated at 220 million years, |
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10"
F6.3 Schmidt Cassegrain Telescope, (1600mm F.L.) Modified Canon
300D camera with Baader IR-UV filter and coma corrector, placed at the scopes prime focus |