Comet ISON has brightened and sprouted a delicate tail of gaseous filaments, streaming away from the sun in our predawn sky. Bright moonlight interferes this week as the comet sinks deeper into morning twilight. This telescopic image was taken  at 5:30 a.m. Friday from Stagecoach.

Jimmy Westlake/courtesy

Comet ISON has brightened and sprouted a delicate tail of gaseous filaments, streaming away from the sun in our predawn sky. Bright moonlight interferes this week as the comet sinks deeper into morning twilight. This telescopic image was taken at 5:30 a.m. Friday from Stagecoach.

Celestial News with Jimmy Westlake: Comet ISON springs to life

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— After lagging behind its projected brightness curve for weeks, Comet ISON suddenly sprang to life late last week and now is the brightest of five comets visible in our predawn sky. This sudden brightening was not totally unexpected. Comet ISON is zooming toward a close encounter with the sun on Thanksgiving, and when a giant snowball hits that solar heat, fireworks are bound to happen.

Jimmy Westlake

Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.

Find more columns by Westlake here.

Let’s recap what we know about Comet ISON. This 2-mile diameter dusty snowball has been hanging out in the distant Oort Cloud of our solar system for the past 4-plus billion years. For some unknown reason — perhaps a close encounter with a passing star millions of years ago — this unnamed, frozen relic from the birth of our solar system was nudged out of its deep freeze and into a million-year free fall toward the sun. It first came to our attention when a robotic telescope of the International Scientific Optical Network recorded a tiny blip on a deep space photograph taken Sept. 21, 2012. Russian amateur astronomers Vital Nevski and Artyom Novichonok spotted the incoming snowball on the photo, and the discovery was announced to the world three days later. At that time, Comet ISON still was far beyond the orbit of Jupiter. On Oct. 1 of this year, Comet ISON passed very close to the planet Mars on its way into the inner solar system. It crossed Earth’s orbit on Oct. 30 and crossed inside Venus’ orbit on Nov. 12. It will cross the orbit of the innermost planet, Mercury, on Friday while traveling more than 150,000 mph. Comet ISON finally will reach its closest point to the sun on the afternoon of Nov. 28, Thanksgiving, only 750,000 miles above its sizzling surface. It is then that the comet’s ices will be exposed to temperatures of 5,000 degrees and should be vaporizing most rapidly. If the snowball holds together, it will slingshot around the sun and head back out the way it came in, hopefully sporting a long tail of dust and gas to dazzle us here on Earth.

When I observed Comet ISON at 5:30 a.m. Friday morning, it had finally grown bright enough to be seen with the unaided eye and had sprouted a very delicate tail of gaseous streamers. This was at least a 10-fold increase in brightness compared with previous mornings. Comet ISON is finally responding to the ever-increasing solar heat as it plummets sunward. I remain hopeful that a beautiful naked-eye comet is in our future.

In a few more days, as it makes a beeline for the sun, Comet ISON will be lost in the morning twilight to observers here on Earth, but it will come into the sights of NASA’s sun-watching STEREO spacecraft Thursday. Then, we can all watch through STEREO’s eyes what happens to Comet ISON as it rounds the sun. Will it crumble and vaporize in the intense heat, or will it hold together and reappear in our morning sky after Thanksgiving as a naked-eye spectacle? Only time will tell, but in the meantime, you can see daily updates and photographs of Comet ISON at www.spaceweather.com.

Keep your fingers crossed!

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. His Celestial News column appears weekly in the Steamboat Today newspaper and his Cosmic Moment radio spots can be heard on KFMU. Check out Jimmy’s 2014 Cosmic Calendar of sky events at www.jwestlake.com. The calendar features twelve astrophotographs and a day-by day listing of celestial events in 2014. Proceeds from the sale of the calendars benefit the CMC SKY Club.

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