Jimmy Westlake: Prospects dimmer for Comet ISON
September 2, 2013
Comet ISON, the potential "super comet" discovered last year, is not brightening as much as comet watchers would like to see as it approaches the sun. If this trend continues, then the comet might not live up to the most optimistic predictions.
But don't be too concerned — it still has the potential to become one of the brightest comets seen in these parts since Comet Hale Bopp in 1997. Comet ISON still is more than twice as far from the sun as Earth and now is about magnitude 13. This puts it within reach of many backyard telescopes, and it might reach naked-eye brightness in mid-November.
Comet ISON is named for the automated telescope that first photographed it, the International Scientific Optical Network, or ISON. The humans who first recognized the comet on the robotic telescope's images were Russian amateur astronomers Vital Nevski and Artyom Novichonok. According to the rules of the International Astronomical Union — the body who has the authority for naming all things celestial — the comet is named after the automated telescope that first photographed it rather than the two humans who first spotted it in the images. So, we have Comet ISON instead of Comet Nevski-Novichonok. It certainly rolls off of the tongue more easily.
Excitement about its discovery grew rapidly last year when it became clear that Comet ISON would pass exceptionally close to the sun on Nov. 28, 2013, and then swing by the Earth just a few weeks later. As it makes its sizzling, hairpin turn around the sun, the icy comet might be visible in daytime skies beside the sun. It will fade somewhat as it recedes from the sun, but it will approach within 4 million miles of Earth shortly thereafter. The potential for an amazing comet spectacle still is there but not certain.
Comets that approach the sun for the first time, like Comet ISON, apparently are coated with a layer of very volatile ice that quickly boils away while the comet still is far from the sun. This sudden brightening alerts astronomers to the approaching snowball, but as soon as this layer of volatile ice is gone, the comet settles down and sometimes does not become very active. Some do — some don't. Predicting the behavior of a comet months before it arrives in the inner solar system is treading on thin ice. Still, when you consider that this big snowball is going to pass a mere 725,000 miles above the solar furnace, you know something wild is going to happen. Exactly what remains to be seen.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Westlake's astrophotography website at http://www.jwestlake.com.