Ptolemy’s Little Cloud

Open Cluster M 7 Ptolemy’s Little Cloud

This open cluster M 7 (NGC 6475) is of my summer favorites. On the first evening in July last month I made a sketch of this open cluster but I was less than pleased with the outcome. On Friday evening August 6, 2010, I made another attempt to capture the cluster as it crossed the meridian at 9:45 pm local time.
From my location this cluster is never more than 14° above the visible horizon, yet it is an impressive object in the eyepiece despite the thick atmosphere so close to the horizon. It was described as a “little cloud” following behind the stinger of the scorpion by Ptolemy nearly 1900 years ago. At about 800 light years away and slowly getting closer to us, this young 200 million year old collection of associated stars spanning 20 light years across is an impressive sight in binoculars or telescope.

Sketching:

M 7 in Scorpius
R.A. 17h 55m, Dec. -34° 49′
10″ inch f/5.7 21mm eyepiece at 69x
Sky conditions were good for transparency
Date and Time: 8/7/2010; 2:40 -3:15 UT
9″ x 12″ white Strathmore Windpower smooth paper, # 2HB, # 4HB graphite pencils, plastic Pink Pearl eraser.
After scanning the drawing was cropped and inverted Using Microsoft Office Picture Manager.

Frank McCabe