NGC 2068

Messier 78 (NGC 2068) is the brightest diffuse reflection nebula in the sky, a glowing cloud of dust and gas in the constellation Orion, approximately 1,600 light-years away and about 4 light-years across. It was discovered by Pierre Méchain in January 1780 and catalogued by Charles Messier on December 17, 1780. NGC 2068 is part of the vast Orion molecular cloud complex — the same star-forming region that gives us the Orion Nebula (M42) and numerous other nebulae scattered across the constellation. Unlike the Orion Nebula, which glows by emission (gas ionized by hot stars), M78 shines by reflection: its dust grains scatter the blue light of the embedded stars that illuminate it, giving the nebula its characteristic bluish-white glow.

Two bright blue stars — HD 38563A and HD 38563B — are primarily responsible for illuminating NGC 2068. They are young pre-main-sequence stars, recently formed from the same molecular cloud that M78 is part of and still partially embedded in it. The nebula contains several Herbig-Haro objects — small, shock-lit patches where jets from newly forming stars collide with surrounding gas — as well as a number of T Tauri variable stars, young solar-type stars still in the final stages of gravitational contraction. Several fainter reflection nebulae in the immediate vicinity, including NGC 2071 just to the north, form a small complex of illuminated clouds within the larger Orion star-forming region.

In binoculars M78 appears as a faint, comet-like glow; a small telescope shows a roughly rectangular, bright nebula with two embedded stars clearly visible near its center. This image was taken in 2006 with the Mosaic imager on the Mayall 4-meter telescope on Kitt Peak.