The constellation of Orion the Hunter. Orion is one of the best known constellations in the sky. Four bright stars identify a large quadrangle, at the centre of which lies the Orion's belt, an asterism formed by three bright stars lying in a straight line. The two brightest stars in the quadrangle are Betelgeuse (top left), a red giant star and Rigel (bottom right), a hot blue supergiant. The Great Orion Nebula (M42), one of the very few emission nebulae visible with the naked eye, is seen as round pink patch at lower centre. The faint arc-shaped feature seen at centre left is the Barnard's Loop, a giant bubble of interstellar gas and dust.