Monthly Archives: November 2013

Comet Ison – will it, won’t it?

There’s been much excitement lately around the possible sighting of Comet Ison next month. But what is a comet and why is everyone so excited about Comet Ison?

Comets are essentially large dirty snowballs, made of water, ice, dust and carbon-based compounds. Like planets, they orbit around the sun. But unlike planets, which are much larger and stay at the same distance from the sun, a comet’s orbit is elliptical (oval-shaped). This means they are sometimes closer to the sun than at other times.

When comets are closer to the sun, and therefore hotter, the material in the comet starts to melt into what is called a coma. This gives the nucleus a fuzzy appearance. Coma being Latin for hair, maybe ancient scientists thought the comet looked like it had a messy hairdo! Solar winds cause the coma to blow into a tail. Despite common depictions, tails don’t trail behind the comets but always away from the sun, blown by its winds.Image

What’s so special about Ison is how close it went to the sun. There had been three main theories about what the fate of this “sungrazer” would be. One, the comet could have exploded under the solar pressure. Two, it could have simply fizzled out. But what many of us hoped was that its closer encounter with the sun would give it a very bright tail. The disappointing initial prognosis on Friday was that Ison had “died” and fizzled out but since then there have been indications it might be brightening. We’re no wiser than we were before its brush with the sun!

If we’re lucky, the once-in-a-lifetime sighting of Comet Ison will begin in early December. Do send us any great pictures you get!

Another well-known comet is Halley’s Comet, which appears every 76 years. The most famous instance was just before the Battle of Hastings (as depicted left, in the Bayeux Tapestry) where William the Conqueror defeated Harold. Harold ignored warnings that it was a bad omen, however the comet became a portent of fortune for the victorious William! We won’t see Halley’s Comet until 2061.Image

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