As it flares out of the distant Oort Cloud, the newly discovered comet C/2012 S1 (ISON)
appears to be heading on a trajectory that could make for one of the most spectacular night-sky events in living memory. Why is this comet expected to be so unique? Two reasons:
Astronomers predict that the comet will pass just 1.16 million miles from the Sun as it swings around its perihelion, or closest approach. (This may seem like a lot, but remember - the Sun is big. If we were to scale the Sun down to the size of Earth, the comet would pass well within the orbits of dozens of satellites.) The close approach will melt enormous amounts of the comet's ice, releasing dust and gas and forming what should be a magnificent tail.
After it loops around the Sun and forms this tail, the comet should then pass relatively close to Earth
- not near enough to cause any worry, but close enough to put on a great show. Viewers in the Northern Hemisphere will get the best view as the comet blooms
in the weeks approaching Christmas 2013. The comet could grow as bright as the full moon.
Of course, comets have a habit of not living up to expectations
. This one could be sucked into the Sun during its close approach, or not grow as much of a tail as astronomers hope.
But that hasn't dampened enthusiasm for what Astronomy Now is awkwardly calling "a once-in-a-civilisation's-lifetime" event.
The comet expert John E. Bortle is already comparing ISON
with the Great Comet of 1680
, which, according to contemporary accounts
, caused the people of New York's Manhattan Island to be "overcome with terror at a sight in the heavens such as has seldom greeted human eyes.... In the province of New York a day of fasting and humiliation was appointed, in order that the wrath of God might be assuaged.
We can only hope for such a show.
The good news is that it looks like we are certainly going to get a great show... the bad news is that even if the comet body itself comes nowhere near us, it is only a matter of time before Earth interacts with the enormous quantity of debris it leaves in its wake. The wrath of the gods might once more need to be assuaged, portending a bad day for the Powers That Be.
Here is the full text of the 1680 comet description quoted above:
The Dutch and Quaker Colonies in America by John Fiske
Chapter XI, 'New York in the Year 1680'
Late in the autumn of 1680 the good people of Manhattan were overcome with terror at a sight in the heavens such as has seldom greeted human eyes. An enormous comet, perhaps the most magnificent one on record, suddenly made its appearance. At first it was tailless and dim, like a nebulous cloud, but at the end of a week the tail began to show itself and in a second week had attained a length of 30 degrees; in the third week it extended to 70 degrees, while the whole mass was growing brighter. After five weeks it seemed to be absorbed into the intense glare of the sun, but in four days more it reappeared like a blazing sun itself in the throes of some giant convulsion and threw out a tail in the opposite direction as far as the whole distance between the sun and the earth. Sir Isaac Newton, who was then at work upon the mighty problems soon to be published to the world in his Principia, welcomed this strange visitor as affording him a beautiful instance for testing the truth of his new theory of gravitation. But most people throughout the civilized world, the learned as well as the multitude, feared that the end of all things was at hand. Every church in Europe, from the grandest cathedral to the humblest chapel, resounded with supplications, and in the province of New York a day of fasting and humiliation was appointed,in order that the wrath of God might be assuaged.
's choice of words is interesting... A re-examination of history in light of cyclic catastrophes reveals "once-in-a-civilization" events to be such because they are civilization-ending