Object name: M046

Designation(s): M046, NGC 2438,

M46 is another open star cluster but in the winter skies rather than summer. It also is quite low as seen from in the Great (now) White North. It has a planetary nebula on the northern edge, NGC 2438 though the two are totally unrelated. The open cluster is about 5400 light-years away while the planetary is much closer at 2900 light years. The very blue faint star is the white dwarf created when it puffed off its outer layers creating the planetary nebula. Its ultraviolet light provides the energy to make it glow. The cluster is about 300 million years old, the planetary less than 10% that age. In astronomy, these are very "new" objects! You can read more about them at:

While I quoted a distance of 5400 light-years above as that's what a lot of sites say including SEDS linked to above, the astronomers at APOD put it at 5000 light-years while WEBDA says 4500. APOD puts its age at 300 million years while WEBDA says 245 million and SEDS doesn't hazard a guess.

M46 was discovered by Charles Messier on February 19, 1771. NGC 2438 was discovered by William Herschel on March 19, 1786. It is in the original H400 observing program. I logged it for the program on March 23, 1985 on an average night with my 10" f/5 at up to 180x. My entry reads: "Looks a lot like a faint version of M57. The real central star is not seen but a member of M46 does appear a bit off center in the dark area of the ring along with another member star on the inside of the dark area of the ring. This nebula stands high power well." The true central star is seen in my image just to the lower right of the bright star mentioned in my entry as a faint quite blue star.

M46 was the very first object imaged after I built my observatory. Though this isn't that image it is a very early image, one of my first color images. At the time I had no idea how to preserve color in stars and kept trying shorter and shorter exposures. Using only 2 minutes for this one which results in a ton of read noise hiding faint detail. I do need to retake it using proper techniques I didn't understand 11 years ago. Also, being an early image the alignment of the camera was off creating rather elongated stars. Beginner's luck didn't apply to this image, unfortunately.

14" LX200R @ f/10 L=10x2', RGB=5x2', STL-11000XM, Paramount ME