12:45 PM | The day of reckoning has come for Comet ISON

ISON[Image courtesy spaceweather.com taken yesterday from the Canary Islands, eastern Atlantic Ocean]

Discussion

On Thursday, Thanksgiving Day, Comet ISON will make its closest approach to the sun flying through the sun’s atmosphere little more than a million kilometers above the solar surface. At closest approach, the core of ISON could rise by as much as 5000° Fahrenheit – a life or death challenge for an icy comet. No one knows if it will survive.

But if ISON makes it out alive, it could provide a great show to the naked eye and possibly even live up to its billing as the “Comet of the Century”. On Friday, professional and amateur astronomers will be searching for the comet as it comes around the sun and then between Thanksgiving and Christmas, it will fly over the North Pole – potentially, a very nice holiday comet.

What makes ISON quite special is that it is a lone traveler originating from a giant population of comets at the very edge of the solar system – the furthest reaches of the sun’s gravity. The distance from the Earth to the sun is an “astronomical unit” or AU. Pluto, as an example, is 40 AU from the sun. Comet ISON began its journey 100,000 AU away from us in a place called the Oort cloud which contains billions of icy, rocky objects. Detected comets from the Oort cloud are quite rare – probably only a handful per century.

For all of human history – at least a million years according to NASA – this comet has been heading towards the sun. We’ll know beginning this Friday, after coming within a hair of the sun, if Comet ISON survives and is ready to put on a great show for us during the month of December.