Apparently, Comet ISON has surged in brightness by 2 magnitudes (6 fold) in little more than 24 hours. If the trend continues, it could be a faint but easy naked-eye object by the end of the week. The sudden uptick in brightness could be caused by a fresh vein of ice opening up in the comet's nucleus. Rapid vaporization of ice by solar heat is a sure-fire way to boost a comet's visibility. Comet ISON is plunging toward the sun for a Thanksgiving Day pass through the sun's atmosphere. Many more of these brightening events could be in the offing--if the comet does not break apart first.
Monitoring is encouraged. Amateur astronomers, if you have a GOTO telescope, enter these coordinates. Dates of special interest include Nov. 17th and 18th when the comet will pass the bright star Spica, making ISON extra-easy to find. Sky maps: Nov. 14, 15, 16, 17, 18, 19.
Pictured from left to right are exploding Comet LINEAR X1, sungrazing Comet ISON, short-period Comet Encke, and the brightest of them all, Comet Lovejoy. All four are visible in binoculars or backyard telescopes, and Comet Lovejoy (mag. +6.0) is visible to the naked eye from dark-sky sites. Comet ISON is actually one of the faintest of the group; only expanding Comet LINEAR X1 (mag. +8) is more difficult to see.
An apparition of so many comets at once is a rare thing, and amateur astronomers are encouraged to wake up early for a tour of the pre-dawn sky. Dates of special interest include Nov. 15-18 when Comet LINEAR X1 passes by the bright star Arcturus, Nov 17-18 when Comet ISON has a close encounter with Spica, and Nov. 18-20 when Comet Encke buzzes Mercury. These stars and planets make excellent naked-eye guideposts for finding the comets. Meanwhile, bright Comet Lovejoy is approaching the Big Dipper; if you can't see it with your unaided eye, a quick scan with binoculars will reveal it.
Sky maps: Nov. 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
Comet ephemerides: Comet ISON, Comet Lovejoy, Comet Encke, Comet LINEAR X1