Comet ISON to make closest approach to Sun tomorrow

Just as millions of Americans are sitting down for their Thanksgiving feast, comet ISON will be fighting for its life. At 1:38 PM EST, ISON will pass just over a million kilometers (680,000 mi) from the surface of our Sun.  Although it now seems unlikely to live up to the billing "Comet of the Century," ISON still represents a unique opportunity to understand strange objects.

 Comet ISON will make its closest approach to the Sun on Thanksgiving.  (Image credit: ESO)

Comet ISON will make its closest approach to the Sun on Thanksgiving.  (Image credit: ESO)

For a largely icy body like a comet, a close approach to the Sun's scorching surface is a frightening proposition.  ISON's outer layers will begin to sublimate away and it may even break up entirely.  I say "may" because we've never seen a comet like ISON before.  It's what astronomers call a 'dynamically-new sun-grazing comet."  Dynamically new means that ISON is making its first trip to the inner solar system and thus its first encounter with the Sun.  It has spent the rest of its life in the Oort Cloud - the Wild West of the solar system, far beyond the planets.  Sun-grazing means that ISON will pass extraordinarily close to the Sun.  There it will experience high temperatures, strong gravitational stresses, and a high velocity.  Such factors could be its undoing.

Since you should never look directly at the Sun, tomorrow is a very poor opportunity to see ISON for yourself.  In a couple of weeks, it will be far enough away from the Sun to be more easily visible to the naked eye.  Tomorrow is a great viewing time if you happen to be a space telescope, however.  The closer ISON gets to the Sun, the brighter it will be, and a number of space-based observatories will be capturing its every move.

If ISON does survive its solar encounter, it will swing around with such speed that it will be flung right out of the solar system.  That makes the next few weeks a once-in-history opportunity to view this object.