The Great Comet of 2013

by Nicholas Mee on October 11, 2012

On 24th September a new comet was discovered by two amateur astronomers – Vitali Nevski in Belarus and Artyom Novichonok in Russia. Comets are discovered all the time and most pass on their way without creating much of a fuss, but this one seems to be rather special.

The End of Civilisation

Comet Hale-Bopp, which gave us our last really spectacular comet display in 1997.

It is thought that the end of the dinosaurs was brought about by the impact of a comet or asteroid, and as recently as 1908 a comet is believed to have flattened large swathes of Siberian forest in the Tunguska explosion. So could this be the end of civilisation as we know it?

The Good News!

The good news is that the trajectory of the comet has already been calculated and: No, we don’t need to worry about Armageddon just yet. The even better news is that the comet will pass the Earth within a mere 60 million kilometres (40 million miles) and it should put on a spectacular show. Before its nearest approach to the Earth the comet will pass extremely close to the Sun, just 1.2 million kilometres (725,000 miles) above the glowing plasma that forms the Sun’s surface.

The official name of the comet is Comet ISON (C/2012 S1). (ISON stands for International Scientific Optical Network.) It is heading towards the Sun from the vast comet reservoir known as the Oort Cloud that surrounds the Solar System. The comet is currently around 930 million kilometres (580 million miles) from the Sun – further from the Sun than Jupiter and over six times the distance of the Earth from the Sun.

Dirty Snowball

Comets have been described quite fittingly as dirty snowballs. The intense heat that Comet ISON will be subject to during its sun-grazing passage will vaporize the material from which it is formed to create a spectacular tail that will point away from the Sun, swept back by the solar wind of particles that constantly stream outwards from the Sun. Some comets, such as Hale-Bopp shown above, have two tails, one formed of gas and one formed of dust. Comet ISON might even break up in the intense heat of the Sun. Whatever happens it will be well worth seeing. At its brightest the comet is expected to be much brighter than Venus – the brightest of the planets. The brilliance of comets is very hard to predict, but current estimates suggest that it might be as brilliant as a crescent Moon and should be visible from November 2013 until January 2014.

Newton’s Comet

The Great Comet of 1680 painted in the Netherlands by Lieve Verschuier.

Comet ISON seems to have a very similar orbit to the Great Comet of 1680, which was one of the brightest comets of the 17th century and is recorded as having an extremely long tail and to have been visible in daylight. Historically this comet was very important. Isaac Newton gave a detailed analysis of it in his great work The Principia, which was published just a few years later in 1687. One of Newton’s main aims was to demonstrate that his theory of gravity could explain the shape of the orbits of the planets. Earlier in the century Kepler had deduced from Tycho’s observations that the planets move in elliptical orbits. Newton showed that the comet’s orbit was also an ellipse, albeit an extremely eccentric one. This was important because it meant that its response to gravity was the same as the planets. And whereas the orbits of the planets have a very low eccentricity and are close to circles, the comet provided an even better test of Newton’s theory as its orbit was extremely elongated. I will be writing more about this in my next book which is about gravity.

Incidentally, Comet ISON cannot be another return of Newton’s Great Comet, as that comet is estimated to be currently over 250 times as far from the Sun as the Earth, so the relationship between the two comets is not yet known.

More Information

The Great Comet of 1680
http://www.jwwerner.com/history/Comet.html

Caroline Herschel, one of the all-time great comet hunters:
http://www-history.mcs.st-andrews.ac.uk/Biographies/Herschel_Caroline.html

Rosetta – the European Space Agency’s mission to explore a comet. (Due to arrive 2014.)
http://www.esa.int/SPECIALS/Rosetta/SEMYMF374OD_0.html

 

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