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Comet ISON and Things that go bump in the night
Columnist: Lou Mayo

Comet ISON and Things that go bump in the night
24 October 2013

For most of human history, the sky has been filled with wondrous points of light impossible to understand but highly predictable. The predictability of the rising and setting sun, lunar phases, appearance and disappearance of constellations, and of planetary movements, were people's clocks and calendars, foretelling seasonal changes and giving comfort to many cultures. But there were things in the sky that could not be predicted and were cause for great concern and fear. Among these were supernova, eclipses, meteor showers, and comets. These apparitions that appeared and vanished suddenly and without warning were almost always viewed as bad omens, threatening lives, predicting destruction, and foretelling the downfall of kings and kingdoms.

Color image of tapestry showing men looking up at comet.
Tapestry of Bayeux (Normandy) with Halley's comet. Text reads ISTI MIRANT STELLA: "These (people) are looking in wonder at the star." Circa 1070.

Supernova, the violent explosions that mark the end of a massive star's life, were completely unpredictable (as they are today) and they were and even with today's technology are, quiet rare as only a small fraction of stars are massive enough to attain supernova status. Supernovae can and probably have posed problems for life on Earth. Gamma ray emission (well, a Gamma Ray Burst or GRB) from supernova explosions are implicated in the Ordovician Extinction Event, about 440-450 million years ago (Mya) that was responsible for the demise of 60 percent of all marine species.

Eclipses (both solar and lunar) are far more visible, frequently observed, and (thankfully) benign. Ancient eclipse lore records animals (dragons (Chinese), Squirrels (Native Americans), etc.) eating the sun or the sun and moon squabbling. There is evidence from ancient Chinese and Babylonian writing that solar eclipses were observed and recorded as early as 2500 BCE. But eclipse prediction was a tricky business. In fact, according to Chinese legend, two court astrologers, Hsi and Ho, were executed because they failed to predict the eclipse of October 22, 2134 BCE. The battle of Hadys in 585 BCE between the Lydians and Medes was halted, according to the Greek historian Herodotus, when the armies noticed a total solar eclipse, instantly, making peace with each other. And of course, there is the famous story of how on one of his voyages to the Caribbean, Columbus used the Feb. 29, 1504 total lunar eclipse to "convince" Jamaican natives to provide his crew with food lest his god would not bring the moon back.

Today, we know that meteor showers are the fine grained dust streams left behind from comets and, in a few cases, asteroids as they orbit the sun. The Earth then passes through this trail of debris at predictable times every year and the result is a meteor shower. Historical accounts of meteor showers viewed them as purely atmospheric phenomena. One of the most famous accountings is of the November 12, 1833 Leonid meteor shower (dubbed "The night the stars fell") which posted hourly rates of over 100,000 meteors (about 30 per second)! Newspaper reports of the time tell of slaves laying down in the fields and praying to god to save them. Some speculate even that the 1833 Leonid meteor "storm" can be credited largely with igniting the revival of Christianity in America in the 1830's and 1840's.

While meteor storms and eclipses come and go relatively quickly, comets, when near the sun, with their long ion tails and dust tails to scatter sunlight, can be visible in the night (and day) skies for many days or even weeks. Here again, comets were thought to be purely atmospheric phenomena until Tycho Brahe measured the parallax of the Great Comet of 1577 demonstrating that it was at least four times more distant than the moon. The appearance of comets was once thought to be a bad omen foretelling death, the fall of kingdoms, illness, even earthquakes! The return of Halley's Comet in 1066, is thought to have predicted the death of King Harold II and the victory of William the Conqueror in his invasion of England. At least for him, it was good luck! The arrival of the Great Comet of 1910 (Also Halley's comet) was met with much fear and mass hysteria by the general public who hid in storm cellars, took comet pills, and held mass prayer vigils to forestall the end of the world.

Comet ISON will be making its first appearance in the inner solar system this November, so no one has seen it before. There had been some thought that it was related to the Great Comet of 1680 (Comet Kirsch) with an orbital period of 333 years but more recent observations show this is not the case. In fact, Comet ISON appears to be in a hyperbolic trajectory which means it will make only one pass by the sun, never to be seen again! Fortunately, comets can now be viewed without panic but with a sense of awe, wonder, and excitement.

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Read More by Lou Mayo

About: Lou Mayo
Photo of Lou Mayo
Lou is a planetary scientist and program manager working for ADNET Systems at NASA’s Goddard Space Flight Center and professor of astronomy at Marymount University.
Read More by Lou Mayo
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