Messier 42, Messier 43
Messier 42 is the Great Nebula in Orion. The Orion Nebula complex is undoubtedly one of the most famous and beautiful areas of the entire night sky. It is easily visible to the unaided eye from a dark location as a patch of brightness surrounding Theta Orionis, the middle star in the sword of Orion the Hunter, the constellation which dominates the winter night sky. Located 1,350 light-years away, this emission nebula glows red predominantly from the light of hydrogen gas excited by energetic newly-formed hot, young, stars in the heart of the nebula. It is the nearest star forming region to our own star, the Sun. The nebula is thought to be 24 light-years across with a mass of approximately 2,000 solar masses. The brightest central portion of the nebula is called the Huygenian Region. It is named after Christian Huygens, one of its early observers. Some green color can be seen visually in a telescope in this region. The Trapezium is a multiple-star system that makes up Theta 1 Orionis, a cluster of newly formed stars at the heart of the nebula. Messier 43 is the comma-shaped nebula just north of the brightest part of the nebula that contains the Trapezium in the center of the image. M43 surrounds the variable star N U Orionis (HD 37061). Note that N U Orionis is not the same as Nu Orionis. N U is two separate letters that designate a variable star. N U Orionis shines with a visual magnitude of 6.5 to 7.6. It has a spectral classification of B 0.5V. M43 was discovered by Jean-Jacques Dortous de Mairan in 1731. The "Fish's Mouth" is the dark nebulosity that separates M43 from the bright portion of M42. It was named by Admiral W. H. Smyth, a 19th-century observer. The bright outside edges of M42 are called the "Wings." The wing on the southeast side (upper left) is called the "Sword." The fainter western wing (upper right) is named the "Sail." The bright area of nebulosity above the Trapezium is called the "Thrust." Some pink color can sometimes be seen visually in a telescope in the wings. M42 is believed to have been discovered by French astronomer Nicolas-Claude Fabri de Peiresc, on November 26, 1610. Charles Messier added to his catalog in 1769. Photographing M42, Henry Draper took the first image of a nebula on September 30, 1880. He used an 11-inch refractor for the photo. Three years later in 1883, Andrew Ainslie Common took 60-minute exposures with a 36-inch reflector that recorded stars and detail that were too faint to be seen with the eye, even through a telescope. This was a tremendous scientific breakthrough. NGC 1977, just below M42 here, is a complex of blue reflection nebulae mixed with dark lanes and a touch of red emission nebulosity. The blue color comes from reflected starlight scattered by dust. This is an outstanding area by itself and would be more well known if not located next to the amazing Orion Nebula. South is up in this image.
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