Expert astrophotographer Michael Jaeger took this spectacular closeup of Comet Garradd last night from his home in Austria. It shows what you can achieve with planning, dedication and the right equipment. Visible in the image are the star-like nucleus, the fuzzy, spherical coma and a straight-back tail. The coma glows green from the excitation of cyanogen gas (related to cyanide) and diatomic carbon, a molecule composed of two joined carbon atoms. Both these compounds light up a beautiful aqua when excited by the ultraviolet light in sunlight.
“In the beginning I was fascinated by the rapidly changing appearance of comets.
This has not changed even after the observation of more than 500 comets,” according to Jaeger’s notes on his website. He’s been following his favorite quarry since 1982 and uses a 10-inch wide-field telescope for photography.
OK, so that’s how to do comet photography in style. In my photo, you get to see it on the cheap. I used a 70mm telephoto lens set up on a tripod to grab a quick image of Comet Garradd last Thursday night the 18th. The field of view is much, much wider, so the comet naturally appears smaller. Everything is trailed in the picture, because I wasn’t tracking the stars with a motor set to the rate of Earth’s rotation. Our photos have one thing in common — both show the green glow of excited molecules.
When UV sunlight strikes cyanogen and C2 molecules, it imparts energy to their electrons, which jump up from a lower orbit about the atom’s nucleus to a higher one. This excited state lasts a very short time before the electrons jump back down to their original level. When they do, they release that energy back in the form of a tiny green photons of light. The cumulative effect of so many billions of atoms with all those electrons hopping back down to their “comfort level” colors the coma a lovely green. Time exposure photos show it very well, but it’s also visible to the eye once a comet becomes bright enough. I begin to see the coloration in my 10 or 15-inch scopes when a comet reaches about 7th magnitude. Garradd is currently very close to that at about 7.5.
Something similar happens in the northern lights. There, oxygen atoms glow green when fast-moving electrons streaming in from the sun strike those atoms and “push” their electrons to a higher level. The re-release of light occurs when the electrons return to their ground state. Speaking of which, solar weather forecasters are predicting possible minor auroras for northern regions tonight and tomorrow night. With the moon rising late, timing is good. Wishing you a cosmically green evening!