The open star cluster M 46 is located in the
constellation Puppis at a distance of approximately 5500 light years. The
apparent diameter in the sky is about 30 arcminutes, comparable to the diameter
of the Moon. The cluster contains about 500 stars and the age was determined to
300 million years. Th egreenish ring at the northern edge of M46 is the
planetary nebula NGC 2438. The overlay of cluster and nebula is a geometric
effect because the distance to NGC 2438 is just about 3000 light years. At the
upper edge of the image there is another, weaker planetary nebula named PK
231.4 + 04.3.
M 46 forms with the
open star cluster M 47 a pretty pair in the sky.
A two-field mosaic can be found
The image left shows a comparison to the full moon.
Click here or the thumbnail at left to load a larger