WRAL WeatherCenter Blog

Comet ISON, 4.5 billion BC - Nov. 28, 2013

Posted December 2, 2013

ISON's green glow graced predawn skies for a few weeks. (Image courtesy of Damian Peach)

Comet C/2012 S1 (ISON), age 4.5 billion, of the Oort Cloud, disintegrated in the Sun's corona on November 28. ISON was born not long (relatively speaking) after our solar system began forming spending most of its life beyond the orbit of Pluto among other icy planetesimals and comets.

On September 21, 2012, ISON made itself known when astronomers Vitali Nevski of Belarus and Artyom Novichonok of Russia discovered it via the telescopes of the International Scientific Optical Network (ISON). As the orbit was calculated it became clear that ISON was heading for the sun. Excitement grew and ISON soon wore the label "comet of the century" While it did not live up to lofty predictions of broad daylight visibility, it captured the attention of astronomers and the public like no other comet has since Halley's in 1986 or Comet Kohoutek in 1973 (2 other comets "of the century".)

Predicting where a comet will travel is relatively easy, predicting what it will do during those travels is far more difficult. Without a detailed understanding of the makeup of the comet's nucleus and a time machine to gather data on what the Sun will do, it's pretty much impossible to predict a comet's fate. As Canadian astronomer David Levy, co-discoverer of Comet Shoemaker–Levy 9, put it:

"Comets are like cats; they have tails, and they do precisely what they want."

ISON's brightness ebbed and flowed during the year long journey to the Sun. Hours before its big day, ISON brightened for a few hours, dimmed significantly and then brightened again to a level rivaling that of Jupiter or Venus.

On what scientists believe is its first visit to the inner solar system, this sungrazing comet ventured through the outer atmosphere within 724k miles of the Sun's surface last Thursday. By Saturday, little more than a cloud of dust remained.
ISON does leave behind a legacy of what comet expert Karl Battams of the Naval Research Laboratory rightly calls "the largest and broadest cometary data set in history compiled by more ground and space-based telescopes than ever before".

ISON is also survived by many other comets, notably C/2013 R1 (Lovejoy). Discovered just a few months ago, Lovejoy is currently visible in the predawn sky to small telescopes or binoculars in dark skies between the constellations Hercules and Boötes. Lovejoy makes its own pass near the Sun on December 22, though from a less perilous 75 million miles.

Looking forward to 2014, C/2013 A1 (Sliding Spring) will pass inside 100k miles of Mars in October at 34.8 miles per second. Preparations are already underway at NASA to observe the comet with Mars orbiters and rovers.

In lieu of flowers, NASA's Comet ISON Observing Campaign asks that you pay your respects with a visit to the Morehead Planetarium to learn your way around the night sky a bit better or the meteorite display at the NC Museum of Natural Sciences to see some of the rocks that fell from it. Those rocks are distant relatives of ISON. So is the one we are standing on.

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