Great Orion Nebula

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Great Orion Nebula or Orion Nebula, or M 42, diffuse nebula, or cloud of gas and dust, located in the constellation Orion. With its brightest parts having an apparent magnitude (a measure of brightness as seen from the earth) of 4.0, the Great Orion Nebula can be seen with the unaided eye as part of Orion’s sword, which hangs from his belt.

The Great Orion Nebula looks like a star when it is seen with the unaided eye, but even a small telescope reveals its cloudy nature. The entire Great Orion Nebula as seen from the earth is about 60 arc minutes wide, or about four times as wide as the full moon. The Great Orion Nebula is about 1500 light-years from the earth and it is about 30 light-years in diameter.

Unlike some diffuse nebulae, which are visible only because they reflect the light of nearby stars, the Great Orion Nebula not only reflects light, but it also emits light. Emission nebulae like the Great Orion Nebula are so huge that they provide enough gas and dust to create new stars. Some of these young stars are so hot and massive that the energy they give off excites the hydrogen atoms in the nebula and makes them glow. Astronomers estimate that the bright center of the nebula is a nursery for about 700 young stars. Using the Hubble Space Telescope (HST) to view this nebula, astronomers have found more than 150 protoplanetary systems, or stars surrounded by a ring of gas and dust that may be the beginning of a solar system.

The Great Orion Nebula was initially thought to be a star, but in 1610 French lawyer Nicholas-Claude Fabri de Peiresc discovered that it was actually a nebula. This discovery was confirmed independently in 1618 by Czech astronomer Rennus Cysatus. In 1769 French astronomer Charles Messier added the Great Orion Nebula to his Catalogue of Nebulae and Star Clusters (1771-1784), a list of astronomical objects that may be mistaken for comets. Because a dark strip of dust unevenly divides the Great Orion Nebula, Messier assigned the nebula two numbers. The smaller part of the nebula is known as M 43, but M 42 is usually assumed to refer to the entire nebula.

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