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Last Updated: Friday, 13 August, 2004, 15:17 GMT 16:17 UK
Clouds dash hope of Perseids show
Perseid meteor shower, AP
The light show was not spoilt by moonlight this year, but clouds
The annual Perseid meteor shower was marred by cloudy skies in many parts of the UK, but still provided some displays of flashing streaks.

The meteors peaked on Thursday 12 and Friday 13 August and should have been visible from a dark location.

Skywatchers were already frustrated on Wednesday night as cloud blocked any chance of seeing the spectacle.

They had been hoping to see an extra surge on Thursday, but there were few reports of cloud-free sightings.

Chance for stragglers

"The weather has been very much against us, so reports from UK have been limited," Neil Bone, meteor section director for the British Astronomical Association told BBC News Online.

It performs better now than on any other nights of the year. There are only a couple of nights a year you can see these
Neil Bone, British Astronomical Association
"But it was the usual good display; there were quite a few bright ones leaving ionisation trails. The numbers were typical like those of 2002's display," he said.

In 2002, the rate was about one meteor a minute.

Mr Bone said there was no way the show could have been described as "disappointing" even though there was no clear view.

"It performs better now than on any other nights of they year. There are only a couple of nights a year you can see these."

He added that if eager skywatchers wanted a final shot at spotting the meteors, they could still go out in the next few nights to see some stragglers.

But December will bring another meteor light show in the form of the Geminids, which can outperform the Perseids.

Extra surges

Meteors are streaks of light in the sky caused by blazing pieces of dust drawn into the Earth's atmosphere from near space.

The annual Perseid celestial event is a firm favourite of skywatchers. In the past, hundreds of meteors per hour have been observed flaring brightly in the night sky.

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.

Last year's event was marred because the Moon was nearly full, drowning out the glow from the Perseids. This year there was little moonlight.

Astronomers expected a faint, extra surge of meteors would occur 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.

Another surge was predicted 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".

Perseids set for sky show
11 Aug 03  |  Science/Nature
Skywatchers treated to celestial display
13 Aug 02  |  Science/Nature

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