A meteor or shooting star is caused when a tiny piece of space rock, no bigger than a grain of sand, enters the Earth's upper atmosphere at tremendous speed. Friction with the atmosphere causes the rock to burn up and produces a brief streak of light across the sky. On any clear night if you wait long enough you will see one or two sporadic meteors. But at certain times of the year the Earth passes through the debris left behind by a comet. The comet may be long gone but the debris trail from its tail will remain in space across the orbital path of the Earth. As the Earth passes through the trail, the debris crashes into our atmosphere and produces a meteor shower. Tonight (Friday 17th) the Earth will pass through the trail left behind by comet Tempel-Tuttle.
Tempel-Tuttle is a short term comet meaning that it orbits the Sun every 33 years, the last time it was in our neighbourhood was in February 1998, it will be back again in May 2031.
Two astronomers working separately, Wilhelm Tempel and Horace Parnell Tuttle discovered it in 1865. There is no danger of the comet ever hitting the Earth but its tail directly crosses the path of the Earth. The encounter will produce maybe 20 to 30 meteors per hour, all appearing to radiate from the constellation of Leo, hence the name, the Leonid meteor shower.
You don't need any special equipment to watch the meteor shower - just lay back in as dark an area as possible, away from any street lights, and look up. You may see meteors anywhere in the sky but if you follow an imaginary line backwards you will find them originating from the 'head' of the lion.
The best time to see the meteors is after midnight when our part of the Earth is pointing directly into the stream. But patience is the key here; it is very unlikely that you will spot a meteor simply by popping your head out of the window during the ad break on TV. You will need at least 15 minutes to allow your eyes to become dark-adapted then lay back and enjoy the show.
In past years the Leonids have produced a meteor storm of hundreds of meteors an hour; in 1966 viewers in the USA reported seeing 40 to 50 meteors per second during a 15 minute span. This year is not expected to be up to that standard but with the moon being out of the way it should still be a good showing.
Remember if you do manage to see a shooting star then make a wish as they always come true!