WRAL WeatherCenter Blog

Comet ISON visible this week

Posted November 6, 2013

An enhanced view of Comet ISON as it passed the orbit of Jupiter (NASA,ESA, J.-Y. Li, Hubble Comet ISON Imaging Team)

Astronomers have monitored Comet ISON (C/2012) since it was discovered last year. Its unusual brightness so far out in the solar system led to a "comet of the century" title and bold predictions of daytime visibility with a tail that stretches across the sky. Will this comet live up to the hype? Some measurements say yes, others say no.

First a bit about comets. They are very different than their more solid asteroid cousins. Comets are icy cosmic rubble piles, leftovers from the formation of the solar system. Each is made up of water ice, dust, rock and frozen gases such as carbon monoxide. Crush up ice from the freezer, some dry ice, add some Windex and a bit sand and gravel into a very rough ball and you've got a pretty good approximation of a comet. Breath on it a bit and you will see how the tail is formed and why it always points away from the sun.

ISON's early discovery offered scientists the rare opportunity to study this sun-grazing comet over months instead of hours before it rounds the sun later this month. NASA and the European Space Agency have eight spacecraft observing the comet. The Mars Reconnaissance Orbiter watched ISON as it passed Mars, while the SOHO and twin STEREO solar observing spacecraft, as well as SWIFT, EPOXI, SPITZER and of course Hubble have tracked and measured the comet and the gasses it leaves behind.

That dirty snowball nucleus of Comet ISON is estimated at a mile or so across but the coma, or sunlit cloud of gasses surrounding ISON, is as big as the continental United States. The thinner cloud extending beyond the coma is larger than Earth itself. Still, it’s been so far away that only the most powerful ground and space telescopes have been unable to capture images, until recently.

By late October, amateur astronomers began capturing images and reporting observations. To see it yourself, head outside around 4 a.m. with a good pair of binoculars or a small telescope. Early Friday morning's forecast for mostly clear skies is your best opportunity this week. Partly cloudy skies in the early hours of the weekend should make ISON visible as well.

ISON is currently visible in the constellation Virgo. Use the easier to find neighbor Leo as your guidepost. Look to the South for the backwards question mark forming the front of Leo the lion then find the brightest star in that constellation, Regulus. About 13 degrees below Regulus is orange-colored Mars, and another 12 degrees below Mars is Comet ISON. The width of your fist with your arm extended fully will give a good idea of what about 10 degrees of the night sky covers.

Look for a soft glow, a fuzzy smudge of light. This is ISON’s coma. If skies are dark enough, a faint tail may be visible as well. The distance between Mars and ISON will continue to increase so look a bit lower the later in the week you venture out to observe.

The closer ISON gets to the sun, the brighter it will be, so if you cant make it out this week, check back on the WRAL Weather Blog for updated information on where to look. If ISON survives its Thanksgiving day trip around the sun (a 50/50 proposition) and the 5,000° F environment it will be subjected to, it is expected to dim as quickly as it brightened over the next year as it exits the solar system.

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