Monday, 11 November 2013

Astronomers anticipate ISON’s arrival

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CometISON CreditNASAThe Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1) from April 10. Track the comet's journey here. IMAGE: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.WHEN Comet ISON was discovered by amateur astronomers in September last year it was quickly dubbed the comet of the century.

Predications of a very close brush with the Sun led many people to speculate that the comet would be brighter than the full Moon and might even be visible during the day.

But since then it has brightened more slowly than hoped and excitement about the comet has dampened.

And with ISON set to grace our skies later this month, WA astronomers have been left wondering—will it live up to the hype?

The problem, according to Perth Observatory astronomical officer Greg Lowe, is that it is impossible to accurately calculate a comet’s brightness.

He says nobody knows how bright ISON will be.

“Comets in general are a bit variable and fickle,” Mr Lowe says.

“You can compute their orbits accurately but you can’t easily compute their brightness.

“That was shown up, for instance, at the time of Comet Halley coming through in the mid 80s.”

ISON is set to be brightest on or around November 29 (Australian time), when the comet will be at its closest to the Sun.

If it does flare, the tail will be visible from Perth in mid to late November, appearing on the horizon in the east-southeast just before daybreak.

But the best view in WA will be afforded to people in the north of the state, where the night is slightly longer during the summer months.

“If the comet doesn't suddenly brighten a lot, observers in southern Australia won't be seeing anything much,” Mr Lowe says.

“Even if it is pretty bright, the coma [head] won't be above the horizon while the sky's dark.

“Northern hemisphere observers have a better chance of seeing some sort of a display because they're heading into winter; their nights are getting longer while ours are getting shorter.”

One person hoping ISON will flare is astrophotographer Vic Levis, who plans to image the comet from the WA outback in late November.

Mr Levis is set to visit Mt Singleton, about 380km north-east of Perth, to photograph the comet and do some deep-sky imaging.  

There, far away from the city lights, he hopes the higher elevation and clear view of the eastern horizon will give him a good chance of capturing the comet.

Mr Levis says nobody knows what ISON will be like but he hopes it will put on a show similar to Comet McNaught a few years ago.

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