Going Green The Cosmic Way

Comet Garradd photographed last night (Aug. 20) in a rich star field in the constellation Sagitta the Arrow by Michael Jaeger. Click the image to visit Michael's website.

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.

Comet Garradd is a the short green streak at top above the constellation Delphinus. Details: 70mm lens at f/2.8, ISO 3200 and 20-second exposure. Photo: Bob King

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.

The Pleiades (lower left), the moon and Jupiter early this morning about 12:30 a.m. Details: 35mm lens, f/2.8, ISO 400 and 15-second exposure. Photo: Bob King

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!

2 Responses

  1. Daniel W. Best

    I love your blog!!!! Your website has done more for helping me to find celestrial bodies then anywhere else. I’m Ranger Dan at a BLM’s Fishermen’s Bend Rec Site in the Cascade Mountains of Oregon and we have a weekly stargazing program in our dark skies. Whereas we set up for the Ring Nebula every week your blog on other summer sites really make the program fun and unique, and I thank you for that 🙂 Last weekend I went to a stargazing event at the Evergreen Aviation Museum, where I initially learned about astronomy here and now help them in their program. This time though I helped the curator find and photograph Garradd and then other astronomers, who were all aimed at the Ring Nebula, were asking me how to find Garradd. I told many about your helpful blog. If you ever find yourself Oregon way come visit us at FishBend!

    1. astrobob

      Wow, Daniel thanks! Your feedback helps me to know if the observing topics are appropriate and useful. I’m very happy you’ve found them helpful. I’d love to head over to Fish Bend. Thanks for the invite!

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