Satellite operators are holding their breath to see whether the meteors, many just tiny dust fragments, will damage any of the 500-odd satellites orbiting the Earth. The crew members of the Mir space station are also taking precautions against any impact.
Forecasters are predicting cloudy weather for half the country tonight, when the bright trails of the Leonid meteors - caused each year since the 10th century by the Earth passing through the dust left over from the trail of Comet Temple-Tuttle - would be visible. And while the West Country, west Wales and western Scotland are predicted to have clearer skies, the point in the sky from which the meteors appear to come (known as the "radiant") will not be above the horizon until 11pm. The forecast is that the most intense period of the shower will be between 2pm and 10pm today.
Observatories in Japan are planning "Webcasts" of the display. They will be on the Internet at the Web sites:
/fspace/special/livecam_e.htm from 2pm today.
The US space agency Nasa will also have coverage, at:
http://leonid.arc.nasa.gov from an aircraft that is flying over Japan, trying to estimate how much meteor material actually enters the atmosphere during such a storm.
Teams of satellite controllers on the ground will also be watching for any effect on the valuable equipment orbiting the planet. Though the European Space Agency estimates that the chance of any satellite being hit is less than 0.1 per cent, the meteors are travelling so fast - roughly 160,000mph - that they could hole a satellite, potentially disrupting telephone, radio or TV channels. Sky TV is among those at risk.
"Operators are taking damage limitation measures," said a spokeswoman for the British National Space Centre yesterday. "They are switching off high-voltage systems and putting ground controllers on alert." During the storm the Hubble Space Telescope's delicate mirror will be turned away from the particles, while the three cosmonauts on Mir are ready to go into the Soyuz escape pod if the shower threatens the space station.
The last Leonid storm was in 1966, when the shooting stars appeared at a peak rate of 150,000 per hour. But the risk to satellites then was minimal because so few were aloft. Now, with more than 500, the risks are greater. The particles can create an electric discharge that wrecks the delicate electronics on a communications satellite.
Most of the particles, though, simply burn up as the hit the Earth's atmosphere, turning white-hot - to give what ground observers see as a "shooting star".Reuse content