SA sky watchers in for a visual treat

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iol scitech dec 13 Geminid meteor shower REUTERS File photo: A meteor shower lights up the sky over the Mexican volcano Popocatepetl near the village San Nicolas de los Ranchos.

Cape Town - Sky-watchers will be hoping for a clear sight of the heavens this evening and particularly early on Friday, when there should be a spectacular display of “shooting stars”.

This will be the Geminid meteor shower, one of the two best of the year, and conditions are favourable for viewing from South Africa, says astronomy columnist Case Rijsdijk.

But viewers will have to find a dark spot to watch away from the city lights and light pollution, if they want to make the most of the event.

The meteor shower is caused by Earth passing through a “river of rubble” streaming hundreds of millions of kilometres out in space, behind a small asteroid named 3200 Phaethon, although the shower takes its name from the constellation Gemini, explains the Sky & Telescope website.

“If you trace each meteor’s direction of flight backward far enough across the sky, you’ll find that this imaginary line crosses a spot in the constellation Gemini, near the stars Castor and Pollux (the twins).

“This is called the shower’s radiant. It’s the perspective point from which all the Geminids would appear to come, if you could see them approaching from the far distance, rather than just in the last second of their lives, as they dive into Earth’s atmosphere.”

Viewers might see as many as one “shooting star” every minute.

These streaks of light are not from stars, but are caused by bits of rocky debris, ranging from grains of sand to pebbles the size of peas, travelling at a speed of about 35km a second, that are vaporised as they strike Earth’s atmosphere at a height of between 80km and 130km, creating a white-hot streak.

Sky & Telescope says Geminids can appear anywhere in the sky.

“Small ones appear as tiny, quick streaks, while occasional brighter ones may sail across the heavens for several seconds, leaving a train of glowing smoke.”

The Geminid shower was the first to be linked to an asteroid. Although discovered in the 1860s, it was only in 1983 that astronomers identified Phaethon as the source.

According to US space agency Nasa, a new meteor shower could also make an appearance this week, adding to the spectacle. This shower is Comet Wirtanen, and the dust hitting Earth’s atmosphere could produce as many as 30 shooting stars an hour. - Cape Argus

l Online at http:stardate.org/nightsky and http://www.SkyandTelescope.com/meteors

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