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A black background is filled with small, reddish-orange stars. Larger blue-white stars are scattered across the image, with a slightly higher concentration at upper left.
Hubble · Messier 7 · NASA, ESA, D. Bennett (University of Maryland), and K. Sahu (STScI); Image Processing: Gladys Kober

Ptolemy's Cluster

Star cluster in Scorpius · 980 light-years

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TypeStar cluster
ConstellationScorpius
Right ascension17h 53m 51s
Declination−34° 48′
Object distance980 light-years
Apparent magnitude3.3
Apparent size22.2′ (arc-minutes)
Approx. true diameter6.3 light-years across
Also known asM7 · NGC 6475
Messier 7, popularly known as Ptolemy's Cluster, is a star cluster (also catalogued as NGC 6475) in Scorpius — a gravitationally bound family of stars sharing a common origin. It was recorded by Charles Messier in his famous catalogue of 110 deep-sky objects. It spans roughly 22.2 arc-minutes on the sky. At about magnitude 3.3, it is bright enough to glimpse with the unaided eye under a dark sky.

Although it appears about 22.2′ wide on the sky, its real span is roughly 6.3 light-years — the difference is a measure of how far away it lies.

Observing Ptolemy's Cluster

Ptolemy's Cluster lies in the constellation Scorpius and is best placed in the evening sky around June. Its maximum altitude above the horizon depends on your latitude. It is best placed for observers in the southern hemisphere, and sits low for those far north. At its brightness it can be found with the unaided eye under a dark sky and is easy in binoculars.

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Sources

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