Acrux, NGC 4609 and part of the Coalsack

Click for hires

The Coalsack is one of the most famous dark nebulae of the Southern Hemisphere. It lies near Alpha Crucis (Acrux), the main star of the Crux constellation, a double star with nearly equal blue components separated by 4". At 2° to toward East (here at right) a small open cluster is present, NGC 4609.

Technical data
Optics Pentax 75 apo refractor
Focal Length 500 mm
Focal Ratio f/6.7
Exposure Time 1 h 10 min (single exp of 10 min)
CCD Canon EOS 5D with Baader filter
Sensitivity 800 ISO
Location Tivoli Farm (Namibia) at 1350 m height
31 August 2011
Mount Kenko NES
Tracking Lodestar with a small refractor (F.L. 100 mm, aperture 23 mm)
Temperature and humidity T= +14°C, RH=27%
Sky brightness at zenith (with SQM-L) 21.6 mag/arcsec^2 (Moon low on the horizon)
Notes 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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