Sunday, December 18, 2011

An Incredible Week!

Similar to the philosophical conundrum about falling trees in the woods making a sound, if no one observes something happen, did it?   But in the 21st century of advanced technology, instant communications and cameras on every corner, it is difficult for anything to go undetected.

This last week something amazing happened, undetected from the earth.  But with an armada of sun-observing spacecraft, Comet C/2011 W3 Lovejoy was observed to dive into the hellish temperatures of the sun, skim the surface and for the first time ever observed, survived to retreat to the frozen outer solar system. 

The primary observing platform was SOHO - the Solar and Heliospheric Observatory.  Originally designed for a 2-year service life, it was launched over 16 years ago.  It observes the sun with a dozen instruments, including detailed observations of the surface in the extreme ultraviolet and X-ray wavelengths, and the near-sun environment with coronographs.  The coronographs show the outer atmosphere of the sun, storms of charged particles thrown out by active areas on the sun, and most importantly, the near-sun environment, including comets.

Now comets generally are their brightest near the sun, but it wasn't until SOHO's observing station was deployed just how many comets there were.  It has found more than 2100 comets the last 16 years!  It puts to shame the 20 or 30 found from the earth's surface.  The majority of those found from SOHO are a special type called Kreutz sungrazers - from the deepest reaches of the solar system, they dive to within a few tens of thousands of miles of the sun's surface, most all vaporizing and not coming out.  Interestingly, these sungrazers share a very similar orbit - they are all considered pieces of a much larger comet that broke up perhaps 8 or 9 hundred years ago.

On November 27th, Terri Lovejoy, observing in Australia, discover a smudge of a comet that was officially named for him on 2 December, the 16th anniversary of SOHO's launching.  It was the first Kreutz sungrazer discovered from the Earth' surface in over 40 years.  Predicted to reach the brightness of Venus or brighter (about magnitude -5 to -6), most everyone agreed it would never survive it's close approach to the sun and come out the other side, but sometimes the experts are wrong!

As it swung past the sun (on my birthday!) the tail inexplicably was swept away, but the comet survived and the tail redeveloped.  The "experts" are now saying the comet is larger than the 200 yards diameter they estimated, or it would have vaporized.  It now lives to return in another few hundred years.  Some of the other spacecraft observed other aspects of it's pass, such as the Stereo (Solar Terrestrial Relations Observatory) and SDO (Solar Dynamics Observatory).  A really good synopsis of observations and early analysis is located at a Sungrazing Comets Site.

As for future ground-based observations - it might be seen from the southern hemisphere as it moves south and fades, but our friend Andrew Cooper, observing from his workplace on Mauna Kea, Hawaii, was one of the rare observers to have recorded it near perihelion.  Yes, SOHO sees a new comet every 3 days or less (!) but there are still some surprises out there yet for us to find.  And being able to surprise the experts is a thrill too!

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