NGC 2438 is a planetary nebula in Puppis that seems to float inside the open cluster M46, though it is a chance alignment and not a member of the cluster.
At a glance
| type | nebula |
|---|---|
| distance from the Sun | 2,770 light-years (849 pc) |
| its light left it | 2,770 years ago |
| size in the piece | about 0.54 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About NGC 2438
NGC 2438 is a planetary nebula, a ring of glowing gas cast off by a dying star whose hot core now lights it up. In a telescope it appears as a small round ring near the northern edge of the rich open cluster M46, and the pairing is one of the prettier sights of the winter sky. It was natural to wonder whether the dying star had been born in the cluster.
It was not. The nebula’s velocity along the line of sight differs from that of the cluster’s stars, and distance estimates place it well in front of M46. The two only line up from where we stand. The nebula also has a faint outer halo beyond its bright ring, gas lost by the star in an earlier phase.
What you see in the piece
Fly between the two and the illusion breaks: here the nebula sits much nearer the Sun than the cluster it appears to belong to from Earth.
Questions
Is NGC 2438 part of M46?
No. NGC 2438 lies in front of M46 and moves at a different velocity; it is only aligned with the cluster from our point of view. It is 2,770 light-years (849 pc) from the Sun.