|Right Ascension||05 : 46.7 (h:m)
|Declination||+00 : 03 (deg:m)
|Visual Brightness||8.3 (mag)
|Apparent Dimension||8x6 (arc min)
Discovered 1780 by Pierre Méchain.
M78 is the brightest diffuse reflection nebula in the sky. It belongs to the Orion complex, a large cloud of gas and dust centered on the Orion Nebula M42/M43, and is about 1,600 light years distant. It is the brightest portion of a vast dust cloud which includes NGC 2071 (northeast, lower right in our image), NGC 2067 (close northwest), and very faint NGC 2064 (southwest), all visible in our image. Together with some other nebulae, including NGC 2024 (Orion B) near Zeta Orionis (sometimes called the Flame Nebula), all these nebulae are associated with the molecular cloud LDN 1630 (from Lynds' Catalogue of Dark Nebula), a part of the Orion complex.
As a reflection nebula, M78 is a cloud of interstellar dust which shines in the reflected and scattered light of bright blue (early B-type) stars, among them the brightest, HD 38563A, and second-brightest HDE 38563B, both of about 10th visual apparent magnitude. The nature of M78 as a reflection nebula was discovered by Vesto M. Slipher of Lowell Observatory in 1919 (Slipher 1919) At its distance, M78 measures almost 4 light years in extension.
In and near this nebula, 45 low mass stars with hydrogene emission lines, irregular variables similar to the star T Tauri, were detected. Stars of this type are main sequence stars which vary in brightness (by about 3 magnitudes) and spectral type (which is about F or G, and similar to the chromosphere of our sun), are 4 to 5 times brighter than their spectral type would suggest, and associated with nebulosity which may be bright or dark. Probably these are very young stars which are still in their formation process.
Infrared investigations have given a clearer image of the cluster of young stars which have formed in this nebula. From 2.2-micron investigations of the Molecular Cloud associated with M78, LDN 1630 (Orion B), performed with Kitt Peak National Observatory's 1.3-m IR telescope Lada et.al. (1991) concluded that much of the young, embedded star formation is occurring in clusters, including the formation of lower mass stars. A large number of dramatic Herbig-Haro outflow sources, presumably young embedded stars, are found in the region of M78; discoveries by Zhao et al. (1999) brought their number to 17. A gorgeous IR image of M78 and the whole region was created by S. Van Dyk of IPAC with the 2MASS IR Telescope; these data provide an even deeper insight into the star formation process in M78.
M78 is not difficult to locate from Zeta Orionis, also named Alnitak, the easternmost star of Orion's Belt; M78 is situated about 2 degrees north and 1 1/2 degrees east of this star; a chain of 3 stars of mag 5..6, northward from Zeta, may help locating it. Alternatively, it is found roughly 1/2 deg North and 3 3/4 deg East of Delta Orionis, the NW most belt star.
Visually, M78 resembles a faint comet. It is just visible in binoculars under good conditions, as a very dim patch. Small telescopes already show it remarkably bright, and reveal the two illuminating stars, lying North preceding (NW) and South following (SE) like a double nucleus in the compact "comet head" part of M78; suggestions of a short and broad "tail" appear to reach to the South preceding (SW) end. The other nebulae in this field require a very dark sky and are much more difficult to see than M78; under very good conditions, a 4-inch can reveal NGC 2071, and suggestions of haze around M78. Stars are fewer to the west, an indication that in this region dark nebulae seem to obscure the stellar background.
Last Modification: 9 Dec 1999, 22:58 MET