Eskimo Nebula

Caldwell 39, cataloged as NGC 2392, is popularly known as the Eskimo Nebula — named for its resemblance to a face peering out from within a fur-lined parka when seen through a telescope. It is fitting that this planetary nebula rides high in the cold winter sky of the northern hemisphere, shining at magnitude 9.1 from a distance of approximately 3,000 light-years in the constellation Gemini. The bright central star is easily seen even at moderate magnification, surrounded by a well-defined inner disk of ionized gas and the fainter, striated outer shell that forms the "fur" of the parka in the visual analogy.

NGC 2392 is a double-shelled planetary nebula with a complex inner structure. The bright inner disk is sculpted by a fast stellar wind from the central white dwarf, which sweeps outward at roughly 90 km/s and has compressed the surrounding gas into filaments and knots. The outer shell, expanding more slowly, contains a remarkable arrangement of comet-shaped knots — dense clumps of gas with bright heads pointing toward the central star and fainter tails streaming outward — similar in form to the knots seen in the Helix Nebula (C63). This inner-versus-outer shell structure reflects at least two distinct mass-loss episodes in the progenitor star's final years.

This image was taken as part of the Advanced Observing Program (AOP) at the Kitt Peak Visitor Center in 2014. In a small telescope, the Eskimo Nebula appears as a bright blue-green disk — its color coming from doubly ionized oxygen — with the central star visible at around magnitude 10. Under high magnification on a steady night, the inner ring and hints of the outer diffuse halo become apparent, making NGC 2392 one of the most rewarding planetary nebulae to study in detail with a modest instrument.