Straight dope on Comet ISON

In a few days, a highly unusual comet will pass within a million miles or so of the Sun's surface.  That in itself is not unusual.   Comets pass that closely reasonably often and thousands such are known.  However, this comet is a "dynamically new" comet, meaning it has never been close to the Sun before, and no dynamically new comet has come so close to the Sun in at least 200 years.

This rare combination offers an unprecedented chance for astronomers to observe an object which has basically been sitting in a deep freeze since the formation of the Solar System react to close contact with the heat of the Sun.  That in turn will reveal much about what the comet is made of and thus offer clues about how the Solar System itself was formed.  Dozens of major observatories, on Earth and in space, will be watching.

As I write, the comet is visible to the naked eye in the pre-dawn sky, but only if you're in a dark place and know just where to look.  It's a little point of light, not your classic image of a comet.  At least not yet.

While ISON's orbit is known quite precisely, it's not at all clear what happens next.  On November 28th it will reach perihelion, its closest point to the Sun's center.  It will be moving at about 400 km/s, or about 900,000 mph, and experiencing intense heat and significant tidal stress that may or may not destroy it.  If it survives, it may reappear as anything from a point of light to a real spectacle.

If you've seen reports of a "comet of the century" likely to be "brighter than the full moon", this would be it.  The press has a habit of taking the "this could maybe happen if we're really lucky" scenario and running with it.  If you prefer to know what actual astronomers are saying and seeing and what the comet is up to, along with informative discussions of why we don't really know what the comet will do, you'll want to check out CIOC, NASA's Comet ISON Observing Campaign.

CIOC is a coordinating group.  It's not performing the actual observations, but it is a serious scientific collaboration, promoting research and gathering results for all the net.world to see.  This is classic Web, the kind of thing TimBL had in mind, I have to think, when putting up the first HTTP server way back when.

You may be wondering: What kind of a name is Comet ISON anyway?  It's named after the International Scientific Optical Network, a collection of 30 or so telescopes in about 20 countries that has been used in quite a bit of research, including but definitely not limited to detecting the comet in the subject line, formally known as C/2012 S1 (ISON).

UPDATE: Comet ISON appeared to disintegrate just before perihelion, and when it dropped behind the occluding discs of the SOHO (SOlar and Heliospheric Observatory) cameras that have been the main source of images for it in the past few days, the consensus was that there was a good chance that nothing would come out the other side.  When the SDO (Solar Dynamics Observatory) and PROBA (PRoject for On Board Autonomy) scopes that had been pointed at what should have been ISON's path failed to detect anything, the folks at CIOC did the only reasonable thing and declared it dead, vaporized in the heat of the sun (around 2800℃/5000℉).  And then it re-appeared.  At this writing, it is a fuzzy blob headed away from the sun, nowhere near as bright as it had been, but possibly bright enough to be seen with the naked eye when it gets far enough away from the sun.  We shall see.

UPDATE:  ... and it's gone.  On December 18th, the Hubble telescope was pointed at where Comet ISON ought to have been.  We can be quite sure of the location since anything solid remaining would have continued to follow the original orbit -- a solid object moving that fast is not going to be affected significantly by outgassing, the solar wind or other such effects.  The HubbleSite ISON blog has the full details, including photographs annotated to point out things you might think could be comet remains but definitely aren't.  Cosmic rays, stars streaking because the telescope is moving to follow the orbit of the comet, reflections on the lens and so forth.  Plenty of that, no comet.