Comet ISON

by Chris Simmons

On June 2^nd last year several hundred spectators gathered on the front steps of Battle Creek’s Kingman Museum to observe a once in a lifetime astronomical event.  Wearing special solar viewing glasses they, along with millions of others around the world, were treated to the spectacle of the planet Venus moving across the face of the sun.  This “Transit of Venus” will not occur again until 2117.  But if you missed it don’t worry there are always plenty of other once-in-a-lifetime celestial wonders coming along.  One of those many even happen later this year.

In 2012 astronomers discovered a comet dubbed C/2012 S1 (ISON) on a trajectory heading toward the inner solar system.  Comets are actually a common occurrence and sometimes can be rather spectacular.  You might remember Halley’s Comet, which last passed by in 1986 or the even more impressive Hale-Bopp in 1995.  But ISON has the potential to be the most brilliant comet in several hundred years, maybe even rivaling the Great Comet of 1680.

Comets are primarily composed of rock, ice and dust.  They come from a region of the solar system called the Kuiper Belt or even further out in the hypothesized Oort Cloud, both of which are many times further out than the orbit of the most distant major planet Neptune.   They range in size from a few hundred feet up to many miles in diameter.  Occasionally one of these objects is perturbed, perhaps by the gas giant planet Jupiter, sending it on a path toward the sun.  They typically have a very elliptical orbits angled high above or below the ecliptic plane of our solar system.  Their orbits can take from dozens up to thousands or even millions of years to complete.  Halley’s Comet only comes around approximately every 75 Years while ISON is estimated to have been traveling toward us for several thousand years.

As the comets approach the sun they begin to heat up and water ice and other volatile compounds begin to vaporize from their surface.  This forms the distinctive tail called a coma that we can sometimes see from Earth.  ISON is special because is a sungrazer comet, which means its trajectory will bring it very close to the sun.  In fact it is expected to come as close as 680,000 miles from the sun.   If estimates are correct ISON could be as bright as or brighter than the full moon around Thanksgiving.  It may be so bright that it is even be visible during the day! 

If you are interested in staying up to date on exciting astronomical events like Comet ISON and others please visit Kingman Museum.  Planetarium programs schedules can be found at kingmanmuseum.org or “Like” their Facebook page at facebook.com/kingmanmuseum for updates.