Comets and a New Star of Bethlehem


The evening of Monday, March 25, 1996 was crisply cold and clear.  It was quite late. With an early alarm and at least 10 hours of work ahead of me the next day what was I doing driving out of St. Louis toward the dark farm fields of rural Illinois?  The answer, of course, is love. 

I love my husband and he loves astronomy.  We were going to see Comet Hyakutake, an interplanetary traveler who had taken everyone by surprise.  What I saw took my breath away.  Comet Hyakutake was brighter than most stars (magnitude zero on a scale where the smaller the number the brighter the object), with a coma larger than the moon.  Its tail covered 80 degrees of arc; you could not see it all without moving your eyes along its length.  Near the zenith, it was so close you could actually see it move against the star field!  It had a bluish-green color due to its emissions of diatomic carbon.  Celestial beauty does not come any rarer.  

This unannounced visitor had not been near Earth for at least 70,000 years.  That long ago, Mt. Toba in Indonesia had exploded, altering the climate and creating a population bottleneck by killing all but about 15,000 humans.  We did not know Hyakutake was coming until it was sited by a Japanese astronomer on January 31, 1996.  Adding to the amazing surprise of the comet was the fact that it was coming fast and it was close!  Hyakutake came within 10 million miles of the Earth.  That is the astronomical equivalent of a bow shot.   By comparison, Comet Hale-Bopp was 13 times farther from the planet than Hyakutake. 

Now we have another comet coming our way.  C/2012S1 (it needs a better name) will be here in December of 2013.  It is expected to be brighter than Hale-Bopp or Halley’s Comet, but not Hyakutake.  It will be visible from November, 2013 through January, 2014, but, begging comparisons to the Star of Bethlehem, this new comet should be making its closest pass to Earth on December 26, 2013.  All of this, of course, depends on its ability to survive its perilous trip through the solar system. 

Carl Sagan described comets as dirty ice balls.  They are.  The nucleus of a comet is a conglomerate of frozen ice, dust and gas bigger than a small town.   They originate in the Oort Cloud beyond the edge of our solar system and travel in long, elliptical orbits around the sun.  As the comet approaches the sun and the nucleus heats up its coma swells larger than our planet and spews off loosened dust and gasses into its tail.  Pressure from the suns photons and high speed solar particles (the solar wind) pushes the tails ejecta away from the sun.  The meteor showers that we enjoy throughout the year are caused when the planet crosses the path of comet debris left in our orbit. 

Since science seems to be the subject that Americans are least at home with, after economics, this wonderful news will undoubtedly be met with cries of gloom and doom.  All of the apocalyptically inclined who will be sorely disappointed when the Mayan’s don’t correctly call the end of the world on 12/12/’12 will shift their energies to the comet coming the following year.  It is curious that the doomsayers cry, “We’re all going to die.” and then buy dried food and generators. 

Personally, I choose not to worry about things I can not control.

Enjoy the music of the sphere, and keep the faith.    

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