M42, the great Orion Nebula (M42, NGC 1976) , is about 1,500 light years from Earth and about 30 light years in diameter - it is roughly spherical in shape, composed of gas and dust. The colors seen in long exposure photographic images comes from hydrogen, oxygen and nitrogen ionized by the intense energy emitted by the young, bright stars within the cloud. It is also a big object in the sky, extending to over 1 degree in diameter, thus covering more than four times the area of the Full Moon.M42 and the other emission nebula in the universe are stellar nurseries, where gas and dust are condensing into new stars. M42 was cataloged by French astronomer Charles Messier in 1769. It was the 42nd object cataloged by Messier, thus the designation "M42".
Visually, M42 can be observed with the naked eye in areas with dark skies - it is seen as a fuzzy, gray blob in the middle of the "sword" hanging below the prominent triple star "belt" in the constellation Orion. It can be seen with binoculars even in moderately light-polluted skies, and small amateur telescopes make it out easily from most earthly locations. But the human eye lacks sensitivity to low levels of color, so even with the largest telescopes under the darkest skies the nebula appears to be grey.
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