NGC 2438 is a planetary nebula, the gaseous shroud cast off by a dying sunlike star billions of years old whose central reservoir or hydrogen fuel has been exhausted. It is located about 3,000 light-years within the boundaries of the constellation Puppis. It also appears to lie on the outskirts of bright, relatively young open star cluster M46. But NGC 2438's central star is not only much older than the stars of M46, it moves through space at a different speed than the cluster stars. Distance estimates also place NGC 2438 closer than M46 and so the nebula appears in the foreground, only by chance along the line-of-sight to the young star cluster. This image of NGC 2438 shows a halo of glowing atomic gas over 4.5 light-years across, extending beyond the nebula's bright inner ring.
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