You may have heard of a tremendous comet brighter than a full moon expected in our predawn skies next month.
Some have called Comet Ison the “comet of the century,” but that may all be hype.
Comets are basically mountain-sized frozen dirtballs made of ice, dust and rocky rubble that are remnants from the formation of our solar system more than 4.5 billion years ago.
Most comets spend their entire lives in the deeply cold outer reaches of the solar system beyond the planets. Every so often, one or more of these comets break loose and is drawn in toward the inner solar system by the sun’s gravity.
Some comets get caught in very elongated orbits that take them close to the sun and then whip them back out to deep space only to return again.
A good example of that is the famous Haley’s comet that lives in a 75-year orbital cycle. The last time it was by this part of the solar system was in 1986.
Some comets swing around the sun, and then head back to the celestial boonies never to be seen again.
Sometimes comets get too close to the sun and get obliterated by the intense radiation.
What will happen to Comet Ison? No one really knows.
As comets draw closer to the sun they start melting, vaporizing the ice and releasing debris. Then they develop a large cloud around the nucleus called a coma. Tremendous solar winds push gas and debris back until the comet’s tail stretches out.
As comets retreat from the inner solar system their coma clouds and tails shrink and they leave a trail of debris in their wake.
Ison was discovered in 2012 and started brightening way sooner than expected, when it was still far out in our solar system.
Folks in astronomical circles prematurely concluded that this will be an extremely bright comet when it passes by our sun and Earth, but then the brightening stalled.
Virgin comets like Ison have a coating of frozen carbon dioxide and monoxide that briefly flares up and can give a false indication of the comet’s future brightness.
Presently Ison is about halfway between the orbits of Earth and Mars and not visible to the naked eye.
Still, Ison could wind up being a pretty decent comet that may be visible to the naked eye in December if it survives.
On Nov. 28 the comet will reach perihelion, its closest point to the sun, only a million miles away. The intense heat could completely disintegrate it.
Or Ison could hang together and the intense radiation from the sun could vaporize just enough of the ice and free just enough of the debris to make for a really nice comet.
As Comet Ison heads back to deep space we’ll have a chance to see it in the early morning low southeastern sky just before sunrise.
For the first few days of December the comet should be at its brightest, but will rise only about 45 minutes before the sunrise so it could really be lost in the twilight glare.
As the month goes on Ison will rise earlier and earlier in the southeast and may be easier to see. By about Christmas time the show should be over with.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of “Stars, a Month by Month Tour of the Constellations.” Check his website, www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org/.
Talk to us
> Give us your news tips.
> Send us a letter to the editor.
> More Herald contact information.
