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M46

NGC 2437

Proper NamesNone
Messier NumberM46
NGC/IC NumberNGC 2437
ConstellationPuppis
Right Ascension7h 41m 46s
Declination-14° 48' 36"
Distancec.4,900 light years
c.1,500 parsecs
MagnitudeApparent: +6.1
Absolute: -4.8
DiameterApparent: 20'
Actual: 29 light years
Number of Starsc. 3,400
Optimum VisibilityJanuary / February
NotesOne of a group of open star clusters that range through the northern parts of Puppis and westward into neighbouring Canis Major. These clusters are not directly related to one another, and lie at different distances from the Sun on the same line of sight. Some are much more distant than M46, while others (like its bright neighbour M47) are rather closer to the Solar System.

An open star cluster in the northern reaches of the constellation Puppis, falling almost directly eastwards of the brilliant star Sirius in neighbouring Canis Major. In the skies of Earth, M46 appears within about a degree of another open cluster, M47, but this is a line-of-sight effect: at a distance of about 4,900 light years, M46 is more than three times further into space than its apparent neighbour M47.

M46 is also a much richer cluster than M47: it contains more than three thousand stars, making it some much more populous than M47. The stars of this cluster are spread across a region about thirty light years in diameter, with little obvious concentration towards the centre of the cluster.

A distinctive feature of M46 is a planetary nebula, a colourful double ring of material that appears to fall within the northern edges of the cluster. As with M47, this is another line-of-sight effect: the nebula, NGC 2438, is actually only 2,900 light years from the Solar System, placing it far closer than the clustered stars of M46 that form its backdrop.

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