Ori­on the Hunter, the Giant, the pur­suer of the Pleiades, is a famil­iar fig­ure in the night sky. Even the neo­phyte stargaz­er will rec­og­nize the three bright stars of Ori­on’s belt, and the tri­ad of stars that are the sword dan­gling at his hip. If the night is clear you might notice that the mid­dle star of the sword lacks the sharp def­i­n­i­tion of the oth­er stars. Binoc­u­lars will show that the “star” is not a star at all, but a blur of green­ish light. Obser­va­to­ry pho­tographs record a swirling drap­ery of lumi­nous gas.