Messier 46 in Puppis is a rich open cluster with planetary nebula NGC 2438 appearing in front of it.

At 6th magnitude, M46 contains 100 bright stars, the brightest of which is magnitude 8.7. It is almost one-half degree in apparent diameter, the same size as the full moon. It is estimated to be 300 million years old.

Planetary nebula NGC 2438 is one arcminute in diameter and shines at 11th magnitude.

The star visible inside of NGC 2438 is not the true central star that powers the nebula. The central star in NGC 2438 has a magnitude of 17.7, so the star visible inside of the ring is a member of M46, which lies behind the planetary nebula, but along the same line of sight.

NGC 2438 is located at a distance of 2,900 light-years from Earth. M46 is located 5,400 light-years away.

M46 was discovered by Charles Messier in 1771. NGC 2438 was discovered by William Herschel in 1786.

North is to the top in the above image.

M46, NGC 2438 Catalogs: M46, NGC 2437 NGC 2438, PK 231+4.2 Object Type: M46: Open Cluster NGC 2438: Planetary Nebula Magnitude: M46: 6.1v NGC 2438: 10.8v Size: M46: 20' NGC 2438: 76" Constellation: Puppis Image Field Centered At: RA: 07h 41m 40s Dec: -14° 49' 46"