About image
M 46 is a rich open star cluster in Puppis constellation.
Inside the cluster it is visible a small planetary nebula, NGC 2438: but in
reality this is only for a perspective effect, because M46 has a
distance of 5400 light years, while NGC 2438 has a distance of 2900 light
years.
On the image it is visible also another very faint planetary nebula, PK
231+4.1, with magnitude 14.4: you can see it as a little disk at about the
half distance between NGC 2438 and the right side of the image.
