First recorded by Ptolemy in 130 AD
M7 is known as the Ptolemy Cluster. It is classified as an open star cluster in the southern constellation of Scorpius approximately 980 light-years from the Earth. M7 is the southernmost object in the Messier Catalog. For astronomers in higher latitudes, M7 never rises very high above the horizon and is a difficult object to observe. The cluster is one of the brightest in the night sky. At a visual magnitude 3.3 it is a naked eye object and has been observed since antiquity. Visually, with the bulge of the Milky Way directly in line with M7, its stars appear to be embedded in the bright "mist" of the Milky Way. Images, such as the one above, resolve the "mist" into a cloud of almost uncountable stars. The cluster is composed of approximately 80 stars between magnitudes 6 and 10. Most of these are hot, massive, blue stars, however, the brightest member is a yellow magnitude 6 G8-type giant star. M7 spans 1.3 degrees of the sky which equates to approximately 25 light years in diameter.