Comet ISON set to be spectacular in 2013

Astronomers have discovered a new comet that looks like it could – no promises, mind – become a dazzlingly brilliant object at the end of next year, visible in broad daylight and hopefully sporting a spectacular tail when darkness falls.

Comet McNaught
Comet McNaught, displaying a fine tail in January 2007, photographed by S Deries from Chile. Credit: S Deries/ESO

The comet, discovered from Russia by the International Scientific Optical Network (ISON) on 21 September, is currently only visible in the world’s larger telescopes at magnitude +19 as it still lies beyond the orbit of Jupiter. UK amateur Nick Howes, working with Ernesto Guido and Giovanni Sostero from Italy, managed to image the comet using the RAS telescope in New Mexico. Read about their work here.

Calculations show that Comet ISON will pass less than two million km from the Sun at perihelion on 28 November, 2013, which is incredibly close, and could then reach a brilliant negative magnitude of between -11 and -16. That would put it between 100 and a few thousand times brighter than Venus, which is mag -5 at brightest, though its proximity to the Sun might make it difficult to see at its most brilliant. (The Full Moon is around mag -12.7).

But the close approach to the Sun could cause the comet, officially labelled C/2012 S1 (ISON), to break up and in any case such sungrazers can be extremely unpredictable. Comet Kohoutek was a famous example of such a celestial visitor in 1973 that failed to live up to the hype.

Karl Battams of the NASA-backed Sungrazer Comet Project, warned that new comets from the Oort Cloud are notoriously unpredictable. He said on Twitter, where he posts as @SungrazerComets: “Not wanting to ruin the fun, but I should add a note of caution that sometimes comets don’t turn out as planned. It *really could* be as bright as the moon… and equally it *really could* dissipate long before it gets here…”

The discovery of C/2012 S1 (ISON) was made by Vitali Nevski, of Vitebsk, Belarus, and Artyom Novichonok, of Kondopoga, Russia, on CCD images made with a 0.4-metre reflecting telescope near Kislovodsk, Russia.

The new comet’s orbit is nearly parabolic which tells astronomers that it may be on its first trip into the Solar System from the Oort Cloud, a vast reservoir of icy debris surrounding the Solar System. It might therefore eject vast jets of gas and dust and be spectacular with a fine tail and even become one of the finest comets ever witnessed by mankind.

New Comet ISON imaged on 22 September at a faint magnitude 19
New Comet ISON imaged on 22 September at a faint magnitude 19 by Ernesto Guido, Giovanni Sostero and Nick Howes

That is what happened with the last major example of these unexpected arrivals. Comet McNaught (C/2006 P1) became visible in broad daylight in January 2007 when it reached magnitude -5.5 as it rounded the Sun at a distance of 25 million km, much further from the Sun than Comet Ison will be. Days later it sported a magnificent curved tail as seen from the southern hemisphere and was acknowledged to be the best comet for 40 years.

Comet Ikeya-Seki (C/1965 S1) was another sungrazer that reached magnitude -10 in 1965. While astronomers keep their fingers crossed that Comet ISON will become as magnificent as everyone hopes, remember that another comet is also set to put on a resonable show in the night sky next year.

Comet Pan-STARRS (C/2011 L4) which was discovered by an automatic survey from Hawaii in June last year is expected to be bright in the evening sky after sunset next March at a reasonable brightness of up to -1.

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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