Messier 7, Ptolemy's Cluster   HOME INDEX BACK NEXT

Open Cluster in Scorpius 

This large and bright open cluster is fairly easy to spot with the naked eye, just above the tail of Scorpius, the Scorpion. Its discovery is attributed to Claudius Ptolemy in about 130 A.D. Through binoculars, its brightest stars form a rough "X" shape, and through a telescope with a low-power eyepiece, it is stunning sight.

The apparent size of this cluster is typically listed as 80 minutes of arc, which means that only the bright central portion of the cluster is seen in this telescopic image. The full size of M7 can be seen in the wide-field view below. This lower image also shows another beautiful open cluster--Messier 6, the Butterfly Cluster, about 4 degrees to the northwest.

Magnitude 3.3
Apparent Size 80'
Distance (light yrs) 980
Right Ascension 17:53.8
Declination -34 47
Field of View 31' x 24'


Image details:  Exposure times of 6 minutes each of luminance, red, green and blue, taken with an SBIG ST-8300M imager and a 12" Meade telescope at f/6.5.

September 2013

Below: A 6-minute exposure on Kodak Ektar 1000 film using a Canon camera and an Aero-Ektar lens with a focal length of 178 mm. 

July 1992