BLUE STAR MEETS GREEN COMET
Over the weekend, Comet ATLAS (C/2020 M3) passed by the massive blue star Bellatrix, left shoulder of the constellation Orion. Amateur astronomer Bum-Suk Yeom photographed the close encounter from Namwon, South Korea:
"The juxtaposition of blue and green against the black velvet background of space was really quite striking," says Yeom.
Bellatrix is blue because it is hot. Almost 10 times as massive and 10,000 times more luminous than the sun, Bellatrix has a surface temperature of 22,000 K. The juggernaut produces most of its starlight in the form of blue and UV photons. Comet ATLAS is green because it is cold and carbonaceous. The icy comet, slightly warmed by the rays of the distant sun, spews diatomic carbon (C2) into space--a substance that glows green in the frigid vacuum of space.