Telescope Reviews: Binocular Icon 28 : M4, a globular in Scorpius.

M4, the beautiful globular in Scorpius, is one of the closest globular clusters to our sun. With a distance of 7.200 l-y, the globular appears bright and large.
M4 is very easy to locate. Just point your binoculars at Antares. The globular cluster can be seen as a little glowing cloud one and a half degree to the west of Antares. Unfortunately, the scorpion stays low in the south for northern latitude observers.

During a vacation at Mallorca, I visited a dark observation site ( lat. 39° ). From there I had a clear view to the south. No lights were visible, but the sky line was lit up by the coast cities. M4 was not visible with the naked eye. With a pair of 15x70 , the globular’s soft glow was very obvious. I remembered my telescopic observation of a few years back. I then noted a chain of stars running from north to south through the partially resolved cluster. My pair of binoculars did not resolve M4. The bright core, seen with direct vision, was surrounded by a soft halo that gradually faded away in the sky glow. There was a brightening in the cluster’s glow, running from north to south.
Another globular cluster, NGC 6144, is in the same view with Antares and M4. This object was too faint to be seen.

Site : Andratx, Mallorca, Spain
Date : July 25, 2008
Time : around 21.30UT
Binoculars : TS 15x70 Marine
FOV: 4.4°
Filter : none
Mount : Trico Machine Sky Window
Seeing : 2,5/5
Transp. : 4/5
Sky brightness : 20.40 magnitudes per square arc second near zenith (SQM reading).
Nelm : 6.0
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

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