M78 is an often forgotten nebula in the constellation of Orion. It's a reflection nebula that's part of the Orion Molecular Cloud Complex, a large cloud of gas and dust centered on the famous Orion Nebula (M42) and De Mairan's Nebula (M43). Also included in this grouping are NGC 2064, NGC 2067 and NGC 2071 and other nebulae. Reflection nebulae like M78 are clouds of interstellar dust that shine due to reflected and scattered light from nearby stars.
M78 was discovered by Pierre Méchain in early 1780 with Charles Messier adding it to his catalogue on December 17, 1780. Although only of 8th magnitude, finding M78 is easy since it's positioned just a few degrees northeast of Orion's famous belt. The three bright stars that make up the belt are Alnitak (ζ Ori - mag. +1.72), Alnilam (ε Ori - mag. +1.69) and Mintaka (δ Ori - mag. +2.25). Positioned 2.5 degrees northeast of Alnitak is M78.
The nebula is visible in 10x50 binoculars, appearing as a small, faint, hazy patch of light. A small telescope of aperture 80mm (3.1-inch) or large 20x80 binoculars reveal a little more detail, especially the brighter northern part of the nebula, which appears as a comet like fan shape. Also visible, surrounded by the nebula, are a pair of 10th magnitude stars that are responsible for making the cloud of dust visible. Of all known reflection nebulae, M78 is the brightest in the sky. With a 200mm (8-inch) or large scope it's possible to notice brighter areas and twists in the nebula especially when using averted vision.
About 45 variable stars of the T Tauri type, young stars still in the process of formation are known to exist in M78. Faint nebulosity, NGC 2071, lies very close to the north edge of M78.
M78 has an apparent size of 8.0 x 6.0 arc minutes. At a distance of 1,600 light-years this corresponds to a maximum spatial diameter of about 4 light-years. The nebula is best seen during the months of November, December and January
M78 Data Table
|Object Type||Reflection Nebula|
|RA (J2000)||05h 46m 46s|
|DEC (J2000)||00d 04m 45s|
|Apparent Size (arc mins)||8.0 x 6.0|
|Notable Feature||Part of Orion Molecular Cloud Complex|