Telescope Reviews: Binocular Icon 30 : M7 - The Venom of the Scorpion

M7 is, with a declination of -35°, the most southern Messier object. From my backyard, M7 never raises higher then 4.5° above the horizon. I was fortunate to observe this beautiful open cluster from dark observing site during a summer vacation in Spain. M7 and M6 were visible to the naked eye as two brightenings along the Milky Way near the Sting of the Scorpion. M7 was the most obvious, while M6 needed a keen eye to be detected. These two galactic gems were known even before written history. The name that the Arabs gave to these two clusters : ‘The Venom of the Scorpion’, always triggers my imagination.

M7 can not be missed, even when it’s not visible with the naked eye. The beautiful cluster can be found about 4° north-east of Lambda Scorpii. M7 appears very large, with fifteen bright stars scattered over an area of 80’. A bright double star can be seen near the center of the cluster. With averted vision, the number of cluster members can grow to over 50, depending on the size of the used binoculars. The majestic splendor of M7 is best appreciated with small to medium binoculars. This cluster is simply too large for common telescopes. M7 is 800 l-y away and has an integrated magnitude of 3.3.

Note : the initial sketch was created with a resolution of 1600x1600 pixels. Because of the forums restriction, the sketch is resampled to 800x800. This resolution is far inferior to the level of resolution that the human eye is capable of behind the eyepiece. As a result, close (but clearly separated) doubles, like the one in the center of this cluster, risk to become smeared out on the low resolution sketch.

Site : Andratx, Mallorca, Spain ( 39° N )
Date : July 27, 2008
Time : around 22.00UT
Binoculars : TS 15x70 Marine
FOV: 4.4°
Filter : none
Mount : Trico Machine Sky Window
Seeing : 2/5 (the view suffered from heavy turbulences in the air)
Transp. : 4/5
Sky brightness : 21.08 magnitudes per square arc second near zenith (SQM reading).
Nelm : 6.5
Sketch Orientation : N up, W right.
Digital sketch made with Photo Paint, based on a raw pencil sketch.

(Note: if the sketch does look too dark on your monitor, try to darken the room.)

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Rony

My Astronomical Sketches

My Binocular Sketches

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