Orion, in astronomy, a prominent constellation visible from almost the entire earth. (From the North and South Poles only-part of the constellation is visible.) Orion is easily seen in the Northern Hemisphere during the evening in the winter sky It is located south and slightly east of the constellation Taurus. Two of the brightest stars in the sky, Betelgeuse and Rigel, are found in Orion. Near the center of Orion is a bright nebula (a cloud of gas and dust) that is faintly visible to the unaided eye.