Messier 46 or M46 (also designated NGC 2437) is an open cluster in the constellation Puppis. It has an apparent visual magnitude of 6 and its angular diameter is 27 arc-minutes. M46 lies at an estimated distance of 5400 light years. The Equinox 2000 coordinates are RA= 7h 41.8m, Dec= -14° 49´ which makes M46 best seen during the winter. The Messier Winter Star Chart shows the position of all Messier objects visible during that season.

The image above shows the uncropped view of M46 through the ASA N12 Corrected Newtonian Astrograph (North is to the right). The bright star HR 2959 (magnitude 4.96) is about 0.5 degree southwest of M46 (lower left corner).

One of the most noteworthy features of M46 is the planetary nebula NGC 2438 appearing 7 arc-minutes northeast of the cluster's center. The planetary is believed to be a foreground object and not physically associated with the cluster. A 3x enlargement of the above image centered on NGC 2438 appears to the right.

For wider view of this open cluster using the Takahashi E-180 Astrograph, see M46 (TAK E-180) .

The open cluster M46 was discovered by Messier in 1771. According to Kharchenko et al. (2005), the distance of M46 is 4480 light years and its diameter is 26 light years. It contains 500 stars and its estimated age is 500 million years.

For more information, see the Messier Catalog as well as specific entries for M46 in Wikipedia and SEDS.

Messier's Description of M46

February 19, 1771
`A cluster of very small stars, between the head of the Great Dog and the two hind feet of the Unicorn, [its position] determined by comparing this cluster with the star 2 Navis, of 6th-magnitude, according to Flamsteed; one cannot see these stars but with a good refractor; the cluster contains a bit of nebulosity.'

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