Comet ISON, visible in binoculars, now with a double tail

Less than three weeks before comet ISON’s closest encounter with the sun, the comet is now sporting a cool double tail.

Like those of most comets, ISON’s dramatic tail is growing as it moves closer to the sun. That’s because the warmth of the sun is releasing gas and dust that were frozen in the comet’s nucleus.

(If you have a few minutes, check out the the Jet Propulsion Laboratory’s incredible video about this process.)

PHOTOS: Comet ISON journeys through the solar system

A double tail on a comet is actually not such an unusual thing, said Sky & Telescope senior editor Alan MacRobert in an interview with the Los Angeles Times.

“There is a gas tail and a dust tail to most comets,” he said. “And the gas tail can get more complicated and start to fan out. In just the past few days we’ve seen this structure happen with ISON.”

Writing on the website Spaceweather.com, astronomer Tony Phillips explains that ISON’s thin gas tail is being blown off the comet by the solar wind, so it is streaming directly away from the sun. The dust tail is heavier, and less likely to get pushed around by the solar wind, and more likely to stay where it is dropped in the comet’s orbital path.

In other ISON news, the comet is also getting brighter. It is now possible to see ISON through a good pair of binoculars in the dawn sky if you have access to a very dark sky and you know where to look.

“You’d have to know how to use a good sky chart and already know the constellations,” MacRobert said.

He said we still don’t know whether ISON will survive its close encounter with the sun on Nov. 28, Thanksgiving Day, or whether it will break apart after its brush with what he called the “solar blowtorch.”

“Comets are one of the few things in naked eye astronomy that are very unpredictable,” he said.

If you get excited about watching the sky, I salute you, and you should follow me on Twitter.

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