Scorpius Tail (IC 4628)

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Zeta Scorpii is the orange brigh star at lower-left, but the most insteresting object here an open cluster and a nebula. The main open cluster is NGC 6321 and shows a "tail" of stars toward the right: this feature generated the name of "comet cluster" because from northern latitudes it may resemble a comet with a coma (the cluster) and a tail (the nearby stars), transiting very low on the horizon and with the tail pointing up.
The main nebula is IC 4628, at right, but some faint nebulas are present also on the left.
Two other prominent open cluster are present in the field: NGC 6242 at right-middle, and NGC 6268 at right-top.
Behind all those object lies the Milky Way and its star clouds and dark nebulas.

Technical data
Optics Pentax 75 apo refractor
Focal Length 500 mm
Focal Ratio f/6.7
Exposure Time 3h10min (single exp of 10 min)
CCD Canon EOS 5D with Baader filter
Sensitivity 800 ISO
Location Tivoli Farm (Namibia) at 1350 m height
27 August 2011
Mount Kenko NES
Tracking Lodestar with a small refractor (F.L. 100 mm, aperture 23 mm)
Temperature and humidity T= +11°C, RH=28%
Sky brightness at zenith (with SQM-L) 21.7 mag/arcsec^2 (MW at zenith)
Notes North at right.
This image is a collaborative effort of the Namibia 2011 expedition. Processing: Lorenzo Comolli. Images by: Lorenzo Comolli, Luigi Fontana, Giosuè Ghioldi, Emmanuele Sordini.

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