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Meteor show may be 'spectacular'
The annual Perseid meteor shower, which peaks on 12 August, could provide a "spectacular" show this year, experts have forecast.
Sky watchers can expect to see meteors from a dark location on 12 and 13 August after 2330 BST, but they may be treated to two early "surges".
One of these may occur on 11 August at 2200 BST, while another may be visible just before dawn on 12 August.
Unlike last year, there will be little moonlight to spoil viewing.
Even with a density similar to cigarette ash, encountering the upper atmosphere is like hitting a brick wall
Neil Bone, British Astronomical Association
Meteors are streaks of light in the sky caused by blazing pieces of dust drawn into the Earth's atmosphere from near space.
The Perseids are caused when the Earth passes through debris shed by Comet 109P/Swift-Tuttle. This comet travels through the inner planets every 130 years, most recently in 1992.
The annual celestial event is a firm favourite of sky watchers. In the past, hundreds of meteors per hour have been observed flaring brightly in the night sky.
"If you go out on Wednesday and Thursday (or even on Friday) nights and find a dark location, you can expect to see about one meteor per minute on average," said Neil Bone, meteor section director for the British Astronomical Association.
"Sometimes you'll go two or three minutes without seeing anything. At others, you see two or three in quick succession."
Last year's event was marred because the Moon was nearly full, drowning out the glow from the Perseids.
"The main appeal of this year's [Perseid showers] is that they are well clear of moonlight. So if you can get yourself away from street lights, your chances of seeing some meteors are very good," Mr Bone told BBC News Online.
"It's not a city phenomenon, unfortunately. The only option for city dwellers is to get yourself out."
Extra surges
Astronomers think a faint, extra surge of meteors may be visible on 11 August at 2200 BST due to a filament of dust that boiled off 109P/Swift-Tuttle in 1862 and is only now crossing the Earth's orbit.
If predictions are correct, another surge might occur just before dawn on 12 August due to the influence of Jupiter's gravity concentrating some of the fine comet dust.
The Perseids are so called because tracing their tails back in the night sky mostly leads to the constellation Perseus. This contains a point called the Perseus radiant - the perspective point from which the meteors would appear to come if they could be seen approaching from interplanetary space.
The Perseids are sometimes called the Tears of St Lawrence because the saint's feast day falls on 10 August.
Tiny particles
The dust itself consists of particles that are roughly the size of a match head - or a dried pea - that are travelling at around 50km per second. As they enter the Earth's atmosphere, they burn up with a short-lived burst of light, heat and ionisation.
"The particles themselves are tiny. One that's about the size of a dried pea can produce a meteor as bright in the night sky as the planet Jupiter," Mr Bone explained.
"Even with a density similar to cigarette ash, encountering the upper atmosphere is like hitting a brick wall. They give off all the kinetic energy they carry very rapidly.
If you can get yourself away from street lights, your chances of seeing some meteors are very good
Neil Bone, British Astronomical Association
"The whole meteor phenomenon often lasts about one-tenth or two-tenths of a second. But with some of the bigger ones, the ionisation that goes on will sometimes be behind a what's known as a persistent train.
"This is a glowing wake that lasts two or three seconds after the meteor's gone. It can be quite spectacular, like a fading contrail where the meteor has been. The Perseids are quite prone to this because they come in so fast, carrying so much energy."
Mr Bone estimated that about one in 500 to 1,000 meteors during the Perseid showers are as bright in the night sky as the planet Venus. Astronomers call these "fireballs". |
