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M46 is a rich open star cluster in the constellation Puppis. Within a diameter of 28 arc minutes, or about 30 light-years at its distance of 5400 light-years, M46 contains over 150 bright stars and a total population perhaps over 500. M46 is probably around 300 million years old.

It is also noteworthy for the presence of the planetary nebula NGC2438 on its northern edge (up and left of center). NGC2438 is almost certainly not physically associated with M46 due to its probable evolutionary history, its significantly different velocity, and a distance estimate only a little more than half the distance to M46.

Image info

Telescope:  Celestron 9.25" Schimdt-Cassegrain at f/6.3

Focus:  Prime focus

Filter:  Celestron LPR

Mount:  Vixen GPD with Skysensor2000

Camera:  Modified Canon EOS 300D, at ISO400

Guiding:  700mm refractor guidescope, SAC7 camera, autoguided with Guidedog software

Exposure:  Total 44 mins (11 x 240s)

Date:  15th January 2005

Processing:  RAW file conversion, Offset and Dark subtraction, flat fielding, registering and stacking done in IRIS.  Curve stretching and colour saturation enhancement by Luminance Layering in Photoshop CS.


One of the first images taken with autoguiding - there is a slight ovalling of stars in RA due to mount excursions.  I still need to track down the reason for this and eliminate it!


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