Deep Sky Directory
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M42 The Great Orion Nebula diffuse nebula in Orion
Diffuse Nebula M42 (NGC 1976), an emission and reflection nebula, in Orion
Right Ascension 05 : 35.4 (h:m)
Declination -05 : 27 (deg:m)
Distance 1.6 (kly)
Visual Brightness 4.0 (mag)
Apparent Dimension 85x60 (arc min)
Discovered 1610 by Nicholas-Claude Fabri de Peiresc.
Located at a distance of about 1,600 (or perhaps 1,500) light years, the Orion Nebula is the brightest diffuse nebula in the sky, visible to the naked eye, and rewarding in telescopes of every size, from the smallest glasses to the greatest Earth-bound observatories and the Hubble Space Telescope.
It is the main part of a much larger cloud of gas and dust which extends over 10 degrees well over half the constellation Orion. The linear extend of this giant cloud is well several hundreds of light years. It can be visualized by long exposure photos (see e.g. Burnham) and contains, besides the Orion nebula near its center, the following objects, often famous on their own: Barnard's Loop, the Horsehead Nebula region (also containing NGC 2024 = Orion B), and the reflection nebulae around M78. Already impressive in deep visible light photographs, the Orion Cloud is particularly gorgeous in the infrared light.
The Orion Nebula itself is still a big object in the sky, extending some 66x60 arc minutes, thus covering four times the area of the full Moon. This corresponds to a linear diameter of about 30 light years. It is also one of the brightest Deep Sky objects, well visible to the naked eye, so that the present author is wondering that its nebulous nature was apparently not documented before 1610, when Nicholas-Claude Fabri de Peiresc (1580-1637), a French lawyer, turned his telescope to this region of the sky (although Ptolemy, as well as later Tycho Brahe and Johann Bayer had cataloged the brightest stars within it as one bright star - the latter cataloging it as Theta Orionis, and Galileo had detected a number of faint stars when first looking at this region with his telescope earlier in 1610). It was independently rediscovered in 1611 by the Jesuit astronomer Johann Baptist Cysatus (1588-1657) of Lucerne who compared it with a comet he had observed in the same year. The first known drawing of the Orion nebula was created by Giovanni Batista Hodierna. All these discoveries apparently got lost for some time, so that eventually Christian Huygens was longly credited for his independent rediscovery in 1656, e.g. by Charles Messier when he added it to his catalog on March 4, 1769.
Diffuse Nebula M43 (NGC 1982), an emission and reflection nebula, in Orion
De Mairan's Nebula, part of Orion Nebula
Right Ascension 05 : 35.6 (h:m)
Declination -05 : 16 (deg:m)
Distance 1.6 (kly)
Visual Brightness 9.0 (mag)
Apparent Dimension 20x15 (arc min)
Discovered before 1731 by Jean-Jacques Dortous de Mairan.
M43 is actually a part of the Great Orion Nebula, M42, which is separated from the main nebula by an impressive, turbulent dark lane. It was first reported by de Mairan in 1731 as a "brilliance surrounding a star" which he thought was "very similar to the atmosphere of our Sun, if it were dense enough and extensive enough to be visible in telescopes at a similar distance." Charles Messier included in his fine drawing of the Orion Nebula, and assigned it an extra catalog number, M43, on March 4, 1769. Moreover, William Herschel took it into his list with the number H III.1, although normally he careful avoided to assign his numbers to Messier objects. In his 1811 paper, Herschel states to have observed it as early as March 4, 1774, and cataloged it on November 3, 1783.
The diffuse nebula M43 surrounds the irregular young "nebula variable" NU Orionis (HD 37061, attn: "N" "U" Orionis, not "Nu Orionis", i.e. the variable star 2-letter designation, not the Greek letter) of magnitude 6.5-7.6 and spectral type B IV. It seems that M43 is excited to shine by this star, and contains its own, separate small cluster of stars which have formed in this part of the Orion nebula.