This pair of open star clusters in Puppis is a fine view for binoculars (see the
Canis Major page with parts
of Puppis to find the position in the sky). On the left hand side (east) is
rich M 46 (NGC 2437) and on the right hand side the brighter but more loose cluster
of M 47 (NGC 2422). Just north of M 47 lies the small cluster NGC 2423. These
clusters are only aligned by chance, M 46 is believed to be about three times
more distant than M 47. So they are not a physical pair like for example
it is believed today for h and chi Persei. An extraordinary
feature of M 46 is the small planetary nebulae NGC 2438 at its northern border which
can be seen as a reddish smudge on the above tele lens image. However, this nebula is
probably just a foreground object.
See also:
Jean-Claude Mermilliod's open cluster compilations on
M 46
and M 47
Woldemar Götz, "Die offenen Sternhaufen unserer Galaxis", VEB Johann Ambrosius Barth, Leipzig