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calan online Comet ISON, which began its trip from the Oort cloud region of our solar system, will reach its closest approach to the sun on Thanksgiving Day, skimming just 730,000 miles above the sun's surface.NASA is tracking Comet ISON's journey and hosting events to discuss what the public worldwide may see as the comet traverses the sun. For the latest news and information, visit www.nasa.gov/ison.