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M 42

Difuzna meglica - Diffuse Nebula M42 (NGC 1976), an emission and reflection nebula, in orion

Orion Nebula

Rektascenzija 05 : 35.4 (u:m)
Deklinacija -05 : 27 (sto:m)
Razdalja 1.6 (*1000 sv.l.)
Vizual. magnituda 4.0 (mag)
Zorni kot 85x60 (loc min)

Located at a distance of about 1,600 (or 1500) 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.

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, a French lawyer, turned his telescope to this region of the sky (although Ptolemy had cataloged the brightest stars within it). The first known drawing of the Orion nebula was created by Giovanni Batista Hodierna. As this one, subsequent drawings of this object did so poorly represent Messier's impression that he created a fine drawing of the Orion Nebula, in order to "help to recognize it again, provided that it is not subject to change with time" (as Messier states in the introduction to his catalog).

The nebula, on its northern end, is devided by a conspicuous dark lane, well visible in our photograph, which was obtained David Malin of the Anglo-Australian Observatory, and is copyrighted. The small northeastern portion was first reported by de Mairan, and was given an extra number by Charles Messier, M43 (see below also). In the very neighborhood, to the north, there are also fainter reflection nebulae, partially reflecting the light of the Great Nebula. They were not notable for Charles Messier, but labeled later with the NGC numbers 1973-5-7. Here we have a collection of more images of M42, M43, and more images of M42, M43 and NGC 1973-5-7.

M42 itself is apparently a very turbulent cloud of gas and dust, full of interesting details, which C.R. O'Dell compares to the rich topography of the Grand Canyon in his HST photo caption. The major features got names on their own by various observers: The dark nebula forming the lane separating M43 from the main nebula extends well into the latter, forming a feature generally nicknamed the "Fish's Mouth". The bright regions to both sides are called the "wings", while at the end of the Fish's Mouth there's a cluster of newly formed stars, called the "Trapezium cluster". The wing extension to the south on the east (lower left in our image) is called "The Sword", the bright nebulosity below the Trapezium "The Thrust" and the fainter western (right) extension "The Sail". Here we have a small collection of Images of detail in M42, including another nomenclature for the brightest region in the nebula by historic visual observers, as well as a pictorial study of the Trapezium cluster and region by Lowell Observatory images.

The Orion nebula was, continuously since the early times before its refurbishment, a preferred target for the Hubble Space Telescope. One major discovery was that of protoplanetary disks, the socalled "Proplyds" (planetary systems in formation) in these HST images of M42 (these images were used for an animation simulating the approach to a protostar [caption]). HST images of November 1995 have revealed further insight into the complicated process taking place in this "star factory". Hubble investigations of January 1997 have revealed interesting interactions of the young hot Trapezium cluster stars with the protoplanetary disks: Their violent radiation tends to destruct the discs, so that the lower-mass stars forming here may loose the material needed to form planetary systems.

The Orion Nebula is also one of the easiest and most rewarding target for amateur astrophotographers

It is somewhat unusual that the Orion Nebula has found its way into Messiers list together with the bright star clusters Praesepe M44 and the Pleiades M45; Charles Messier usually only included fainter objects which could be easily taken for comets. But in this one night of March 4, 1769, he determined the positions of these wellknown objects, (to say it with Owen Gingerich) `evidently adding these as "frosting" to bring the list to 45', for its first publication in the Memoires de l'Academie for 1771 (published 1774). One may speculate why he prefered a list of 45 entries over one with 41; a possible reason may be that he wanted to beat Lacaille's 1755 catalog of southern objects, which had 42 entries. Messier measured an extra position for a smaller northeastern portion, reported by de Mairan previously, which therefore has the extra Messier number: M43.

Bill Arnett's Orion Nebula M42/43 photo page, info page.

Povzeto po:
Hartmut Frommert (spider@seds.org)
Christine Kronberg (smil@lrz.uni-muenchen.de)

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