Morning comets ISON, Encke and Lovejoy heat up, glow green

Comet C/2013 R1 Lovejoy, discovered last month by amateur astronomer Terry Lovejoy, glows green in this photo taken with a 12-inch telescope. The comet is currently visible in 6-inch and larger scopes in the morning sky. It may show in binoculars by month’s end. Click to enlarge. Credit: Gerald Rhemann

The color green represents hope and life. It’s also a sure sign our three morning comets are heating up and becoming more active as they approach the sun. I don’t know anyone who’s noticed the green color with their eyes looking through a telescope – the comets are all still around magnitude 10-11 and too faint to fire up our color vision – but the camera records their limey appearance with ease.

2P/Encke, which orbits the sun every 3.3 years, is a large, soft puff of light in the constellation Lynx visible in the wee hours before dawn. Glowing at magnitude 10, it will show in binoculars next month. Its coma fluoresces green from molecules released from ice vaporizing in the heat of the sun. Photo taken Sept. 30. Click to enlarge. Credit: Damian Peach

In some of the pictures you can clearly see the color difference between the comet’s tail and its fluffy coma – that’s the bulbous glow surrounding the tiny and invisible comet nucleus at the center of all the activity. Comas form tenuous, temporary atmospheres tens of thousands of miles across around the icy comet nucleus.

Comet star of the year ISON shows a beautiful green coma, bright false nucleus and pale yellow tail in the photo taken Oct. 4 from Austria by astrophotographer Gerald Rhemann. Click to enlarge.

Don’t expect to ever see a bare comet nucleus through a telescope. They’re not only very tiny, typically only a few miles across, but cloaked by dust and vapors boiled away by the sun. The closest you’ll get is the bright spot in the center of the comet called the false nucleus – a compact region where the dust and volatiles are densely concentrated around the true nucleus.

Comet ISON again on the morning of Oct. 5. The green coma is approximately spherical with a short dust tail pointing northwest. Comet ISON glows at around magnitude 11 right now. Click to enlarge. Credit: Michael Jaeger

Tails glow pale yellow from sunlight reflecting off cigarette-smoke-sized dust particles released from vaporizing cometary ices. The Caribbean blue-green of the coma, pretty as it is, originates from toxic cyanogen (a compound related to cyanide) and diatomic carbon (two carbon atoms bonded to one another). When energized by ultraviolet light from the sun, the gases fluoresce an eye-appealing green.

Everyone’s got their eyes and cameras glued to Comet ISON. This photo was shot on Oct. 4 with a 12.5-inch (32 cm) telescope from Payson, Arizona. Click to enlarge. Credit: Chris Schur

In my experience, the eye can’t sense the green until the comets become bright enough to show in ordinary binoculars at around 7th magnitude. When viewed through 8-inch or larger telescopes the color is tantalizing, like the green and blue iridescence sometimes seen along the edges of high clouds.

Comets ISON, Encke and Lovejoy are all predicted to brighten into visible green territory come November. That’s only a few weeks today. We’ll take the good news that all three comets are on track and brightening steadily. Stay tuned for more updates. For the latest brightness predictions, check out Seiichi Yoshida’s Weekly Information About Bright Comets.

5 thoughts on “Morning comets ISON, Encke and Lovejoy heat up, glow green

  1. Lovejoy is doing very well, now ranked above ISON in brightness. ISON is supposed to brighten 1 magnitude by Oct. 21, according to predictions.

  2. The Solar System looks a little bare at say, 11:30 PM, about the time I plan to go to bed. I could look at Uranus, but I am looking forward to the Moon showing itself at that time in a few days.

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