One of the most iconic nebulae in the sky, the Horsehead Nebula in Orion, is part of a large, dark, molecular cloud. Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s. The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming. The two carved-out cavities of the Flame nebula and NGC 2023 were created by the destructive glare of recently formed massive stars within their confines. They can be seen tracing a spine of glowing dust that runs through the image. The Flame nebula sits adjacent to the star Alnitak, the easternmost star in Orions belt, seen here as the bright blue star near the top left of the image.
The Heart Nebula (IC 1805) is some 7500 light years away from Earth and is located in the Perseus Arm of the Galaxy in the constellation Cassiopeia. It was discovered by William Herschel on 3 November 1787. It is an emission nebula showing glowing ionized hydrogen gas and darker dust lanes. The brightest part of the nebula (a knot at its western edge) is separately classified as NGC 896, because it was the first part of the nebula to be discovered. The nebula's intense red output and its morphology are driven by the radiation emanating from a small group of stars near the nebula's center. This open cluster of stars, known as Collinder 26 or Melotte 15, contains a few bright stars nearly 50 times the mass of our Sun, and many more dim stars that are only a fraction of our Sun's mass. The Heart Nebula is also made up of ionised oxygen and sulfur gasses, responsible for the rich blue and orange colours seen in narrowband images. The shape of the nebula is driven by stellar winds from the hot stars in its core. The nebula also spans almost 2 degrees in the sky, covering an area four times that of the diameter of the full moon
Believed to be the cosmic fire of creation by the Maya of Mesoamerica, M42 blazes brightly in the constellation Orion. Popularly called the Orion Nebula, this stellar nursery has been known to many different cultures throughout human history. The nebula is only 1,500 light-years away, making it the closest large star-forming region to Earth making it relatively bright. Because of its brightness and prominent location just below Orion’s belt, M42 can be spotted with the naked eye, while offering an excellent peek at stellar birth for those with telescopes. It is best observed during January. The Mayan culture’s likening of the Orion Nebula to a cosmic fire of creation is very apt. The nebula is an enormous cloud of dust and gas where vast numbers of new stars are being forged. Its bright, central region is the home of four massive, young stars that shape the nebula. The four hefty stars are called the Trapezium because they are arranged in a trapezoidal pattern. Ultraviolet light unleashed by these stars is carving a cavity in the nebula and disrupting the growth of hundreds of smaller stars.
