We recently looked at Castor, the second brightest star in Gemini and a fine multiple star. Not far away, you’ll find the remnants of a dying star, the beautiful planetary nebula NGC 2392. This is one of the youngest-known planetary nebula– only 1,000 years old— and it’s easily visible in a small telescope, even in city skies. In photographs, this nebula looks a bit like a clown’s face; it also resembles the hooded face of a person wearing a parka, so it’s sometimes called the “Eskimo Nebula”
• The Clown Nebula lies just east of the “waist” of Gemini, near the 4th-magnitude star Wasat (which means “middle” in Arabic).
• The nebula lies within the same field of view as the 8th magnitude star HP36370. At low power, you might think these two objects are a double star. But increase magnification beyond 70-80x, and you’ll notice the nebula is the one that looks “fuzzy” and a slightly green in color.
• The small size of the nebula means you can use a lot of magnification without dimming it too much.
NGC 2392 in Gemini (lower left, in cross-hairs)
• If you have a 6-8″ scope or larger, look for the central star of NGC 2392. This Sun-like star is puffing off its outer layers as it runs out of fuel in its core. In a few tens of thousands of years, the nebula will disappear and the star itself will become a hot and faint white dwarf.
• A UHC or OIII filter may improve the contrast of the nebula, especially if you’re under urban or suburban skies. You’ll likely not see the central star if you use the filter. Can you see any structure in the nebula? Perhaps an outer shell? You will not see the “Clown” or “Eskimo” visually.
Good To Know
The Hubble Space Telescope has taken some wonderful images of NGC 2392. The complexity of the glowing ionized gas near the center of the nebula defies explanation. In the outer part of the nebula, HST shows long orange filamentary structures, which may be large comet-like bodies interacting with material ejected from the central star. Here’s a close-up of similar knots in the Helix Nebula.
Point your scope just 2 degrees northeast of the Clown Nebula and you’ll see the charming but overlooked open star cluster, NGC 2420. Use low power, certainly less than 40x, to see the full field of faint glittering stars. A very pleasant object.