The nebula is important because of its sheer size, as it spreads several degrees from Orion’s Belt to his sword. It is also one of the most active regions of stellar formation visible in the night sky, and is home to both protoplanetary discs and very young stars. The nebula is bright in infrared wavelengths due to the heat-intensive processes involved in the stellar formation, though the complex contains dark nebulae, emission nebulae, reflection nebulae, and H II regions.
The Horsehead Nebula (also known as Barnard 33 ) is a dark nebula in the constellation Orion.
The nebula is located just to the south of the star Alnitak, which is farthest east on Orion’s Belt, and is part of the much larger Orion Molecular Cloud Complex. The nebula was first recorded in 1888 by Scottish astronomer Williamina Fleming on photographic plate B2312 taken at the Harvard College Observatory. The Horsehead Nebula is approximately 1500 light years from Earth. It is one of the most identifiable nebulae because of the shape of its swirling cloud of dark dust and gases, which bears some resemblance to a horse’s head when viewed from Earth.
Barnard’s Loop (catalogue designation Sh 2-276) is an emission nebula in the constellation of Orion. It is part of the Orion Molecular Cloud Complex which also contains the dark Horsehead and bright Orion nebulae. The loop takes the form of a large arc centred approximately on the Orion Nebula. The stars within the Orion Nebula are believed to be responsible for ionizing the loop.
The loop extends over about 600 arcminutes as seen from Earth, covering much of Orion. It is well seen in long-exposure photographs, although observers under very dark skies may be able to see it with the naked eye.
Recent estimates place it at a distance of either 159 pc (518 light years) or 440 pc (1434 ly) giving it dimensions of either about 100 or 300 ly across respectively. It is thought to have originated in a supernova explosion about 2 million years ago, which may have also created several known runaway stars, including AE Aurigae, Mu Columbae and 53 Arietis, which are believed to have been part of a multiple star system in which one component exploded as a supernova.
Although this faint nebula was certainly observed by earlier astronomers, it is named after the pioneering astrophotographer E. E. Barnard who photographed it and published a description in 1894.”
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Whether due to collisions with a spiral arm, or through the shock wave emitted from supernovae, the atoms are precipitated into heavier molecules and the result is a molecular cloud. This presages the formation of stars within the cloud, usually thought to be within a period of 10-30 million years, as regions pass the Jeans mass and the destabilized volumes collapse into disks. The disk concentrates at the core to form a star, which may be surrounded by a protoplanetary disk. This is the current stage of evolution of the nebula, with additional stars still forming from the collapsing molecular cloud. The youngest and brightest stars we now see in the Orion Nebula are thought to be less than 300,000 years old, and the brightest may be only 10,000 years in age.
Some of these collapsing stars can be particularly massive, and can emit large quantities of ionizing ultraviolet radiation. An example of this is seen with the Trapezium cluster. Over time the ultraviolet light from the massive stars at the center of the nebula will push away the surrounding gas and dust in a process called photo evaporation. This process is responsible for creating the interior cavity of the nebula, allowing the stars at the core to be viewed from Earth.
The largest of these stars have short life spans and will evolve to become supernovae.
Within about 100,000 years, most of the gas and dust will be ejected. The remains will form a young open cluster, a cluster of bright, young stars surrounded by wispy filaments from the former cloud.
The Pleiades is a famous example of such a cluster.”*
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Visible to the naked eye the Omega Nebula (also known as the Swan, Horseshoe or Lobster Nebula) M17 is in the Milkyway and is aound 4200 light years distance from Earth
RA 18h 22m, Dec -16deg 10′.
Skywatcher Quattro 10″ f4 Newtonian.
Skywatcher AZ Eq6 GT Mount
Orion Short Tube 80mm guide scope & auto guider – PHD2.
Baader MPCC Mark 3 Coma Corrector, UHC-S ‘Nebula’ filter.
Nikon D5300 (unmodified).
Field of view (deg) ~ 1.35 x 0.90.
37 x 100 sec ISO800.
Pixinsight & Photoshop
14 August 2015
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