Orion's 'Physiology'

Despite competition from a nearly full moon, the constellation Orion shines magnificently above the trees in the southeastern sky from Cedar Rapids, Iowa around 8:15 PM, February 18, 2011. The image of the great mythological hunter is composed of many bright stars and some dim nebulae. The bright star at upper left is Betelgeuse, a red giant with an apparent magnitude of 0.43, located some 640 light years away. Shining at 1.62 magnitude at upper right center is Bellatrix. The three diagonal stars making up Orion's belt are from left: Alnitak (1.71 mag.), Alnilam (1.68 mag.) and Mintaka (2.25 mag.). A diffuse nebula (NGC 2024) resides just below Alnitak, but at an apparent magnitude of 10.00 is invisible even to the camera at this exposure of ten seconds at f/5. Within the vertical "sword" (or scabbard) area below the belt are the nebulae NGC 1977 and M42--the Orion Nebula. Left and below the sword is the star Saiph, at magnitude 2.06, and brightest of all at lower right is the blue-white giant Rigel, shining at magnitude 0.15. Rigel resides some 773 light years from Earth.