Geminids meteor shower lights up December skies
This year’s Geminids meteor shower should provide a fittingly spectacular finale to 2015 the International Year of Light, with an estimated 150 meteors an hour expected to light up the moonless night skies.
The astronomical event was at its best when it reached its peak at 2.30AM (AEDT) Tuesday December 15, 2015, morning.
“The Geminids are an annual meteor show visible across most of the world,” said amateur astronomer Dr. Ian Musgrave of the University of Adelaide. “You can see them from Australia in reasonable numbers.”
Meteor showers usually occur as Earth passes through the debris trails left behind by comets.
But the Geminids are a little bit different because they are associated with a five-kilometre-wide asteroid called 3200 Phaethon.
“The intensity of the meteor shower depends on the density of the debris trail, how deeply into it we pass and whether we pass through a single trail or more than one,” Musgrave said.
The Geminids are more likely to put on a good show than any other meteor shower throughout the year, astronomer Dr. Alan Duffy said.
And things are shaping up for a great night show.
“Last night I snuck out and saw a few shooting stars early so that was actually quite exciting. That’s a really good sign that we have a great meteor shower coming tonight,” he told The World Today.
In Australia, the Geminids will appear to radiate from a point in the north — just above the horizon — in the constellation Gemini.
“The further north you are in Australia the higher the radiant (the apparent point of origin) will be, and the more you’ll see,” Musgrave said.
“You should also flick your eyes from side to side because although [the meteors] radiate out of the north, they actually start to burn up a little bit further along their track.”
The amount of meteors you see depends on the Moon. The brighter or fuller the Moon, the less meteors you are going to see.
“This year’s event will be especially good because the Moon sets long before the radiant rises, but remember the more light pollution you have, the fewer meteors you’ll see, so the further away from city lights the better,” Musgrave said.
“While the meteor shower climaxed at about 2:30am (AEDT) on Tuesday morning, you should get a decent display anytime between 1:00am and 4:00am, with a meteor every two to three minutes.
“But they’re a bit like buses, often nothing happens for quite a while, then a bunch will come all at once.”
The most important factor for a good night of meteor watching is the weather — clouds can be the ultimate spoiler.
Often called a rock comet, Phaethon’s debris trail is believed to be caused by the Sun’s enormous heat cooking surface material on the asteroid, causing it to fracture and crack apart, a bit like cracks in dry mud flats on Earth.
Although they are often incorrectly called shooting stars, these tiny grains of rock usually begin to burn up when they hit the thicker atmosphere at altitudes of about 100 kilometres.
“Every year Earth intersects the trail of debris coming from this asteroid and we get to see beautiful streaks in the sky as these tiny fragments enter the Earth’s atmosphere and evaporate due to the heat of entry giving us brilliant streaks of light,” Musgrave said.
“When you see these meteors streaking across the sky you tend to think that they’re quite large, but in fact they’re only about the size of a few grains of sand.”
While meteors from cometary debris tend to look quite fluffy, Geminids meteors are larger and tend to look more solid. They also move more slowly travelling at about 35 kilometres per second, compared to some cometary meteor showers that travel at speeds of up to 72 kilometres per second.
As to whether Musgrave will be making a wish when he sees the first shooting star of this year’s Geminids, his only comment was: “I find it’s best not to wish on space hardware.”
*Adapted from ABC Online
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