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Comet ISON could outshine the moon next year

Scott Sutherland

The newly-discovered Comet C/2012 S1, or Comet ISON will be swinging through the inner solar system over the next year and a half and astronomers believe that as it gets closer to the Sun it may be brighter than the moon and visible during the day.

It is called ISON because it's named after the International Scientific Optical Network in Russia.

Spotted beyond the orbit of Jupiter September 24, astronomers have noted some interesting facts about Comet ISON.

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  • The comet is larger than most, which gives it the potential to be quite spectacular come next November. Some projections have shown that Comet ISON could reach between -10 to -16 magnitude brightness, which has the potential to outshine the full moon (magnitude -13). Its size also gives it the potential to generate very long tails.

  • Its orbit will take it very close to the Sun. It should be just 1.8 million kilometres away from the Sun as of November 28 next year, as it swings under the Sun's south pole. If its as bright as predicted, and it maintains its integrity as it approaches, it may end up being visible during the day.

  • ISON's orbit is very close to that of The Great Comet of 1680 (C/1680 V1), and ISON will pass by Earth at a distance of 60 million kilometres, just a bit closer than C/1680 V1 (63 million kms). C/1680 V1 is about 4 billion kms away from the Sun right now, so Comet ISON is definitely not the same comet. However, the two comets may very well have been parts of the same larger object at some time in the distant past, which would account for their similar orbits.

  • On September 30 next year, Comet ISON's orbital path looks to be lined up straight over Mars' north pole. However, it will miss that direct pass over the red planet by just a matter of a few days, because it doesn't cross over Mars' orbit until October 3. Still, the Curiosity and Opportunity rovers should get a spectacular view of the comet as it passes.

  • Comet ISON's orbit is angled to the north of the ecliptic, or 'invariable plane' of the solar system. If you were to view the solar system from the outside, you would see that all the planets orbit in the same plane (or very close to it). The only time Comet ISON is south of this plane of the solar system is from just before it crosses Venus' orbit, until it swings around the sun.

  • When Comet ISON first crosses Earth's orbit, on November 1 or 2 next year, it will be 'ahead' of Earth, but after it swings around the Sun and starts to head out again, its path will take it almost directly over the Earth on December 30 or 31, hopefully giving us a rather impressive New Years 2014 display.

NASA photo shows when the comet will cross Earth's orbit on November 3.
NASA photo shows when the comet will cross Earth's orbit on November 3.

Right now, Comet ISON should be visible to anyone with a large enough telescope, and can be seen at about 6.5 degrees east of the star Pollux, in the constellation Gemini. It should be visible to smaller telescopes, or perhaps binoculars closer to the end of next summer, but it won't be until late October or early November next year, when it is between the orbits of Mars and Earth, that the real show should begin.

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When a comet is still out beyond the orbit of Jupiter, it is already generating what's known as the 'coma' — an atmosphere of gas generated by the comet ice being melted by the Sun. As it travels between the orbits of Mars and Earth, the heating from the Sun becomes more intense and the comet's two tails begins to form, trailing off behind it - one made of ionized gases that always points direction away from the Sun and another made of dust that is blown off away from the sun, but that curves back along the path the comet is tracing through space. By the time it reaches and passes Earth's orbit, its tails are typically quite well-formed and can be long and bright. With Comet ISON's size, it is possible that its tails could stretch all the way back to Mars.

Unfortunately, this is all just educated guesses, though. From where Comet ISON is now, there's no way to tell for sure what it is going to look like when it gets closer to the Sun. Comets have been known to just fizzle out, regardless of their potential. For example, on August 30, 2011, Comet Elenin — seen as a doomsday comet by some — simply broke up into smaller pieces and disintegrated. So no one wants to say anything too definite or hopeful about Comet ISON just yet. It will all depend on the comet's composition.

I now feel a certain obligation to mention that there's no chance of Comet ISON hitting the Earth.

Not only does Comet ISON first cross Earth's orbit a full 75 days before Earth reaches that point in its orbit, but even if they were timed perfectly to arrive at that point at the same time, with the angle of Comet ISON's orbit, it would just pass harmlessly over the north pole. Also, the second time it crosses Earth's orbit it will also be above the planet, missing us by nearly 65 million kilometres.

So, don't worry if you hear new doomsday prophecies about Comet ISON (maybe the Mayans were off by a year?) and just keep an eye on the skies to see if this new comet can reach its full potential. Oh, and one other thing, with this comet swinging so close to Earth's orbit on its approach to the Sun, it's possible we may see a nice meteor shower in the middle of January 2014, due to the particles left behind from the comet's dust tail.

If you would like to see the orbit of Comet ISON, NASA has a neat java applet that plots it for you, lets you zoom in and out of the view and watch as the planets and comet orbit the sun. Just follow this link.

(Top photo of Comet ISON from Space.com)