A meteor from the Leonid meteor shower, visible as a diagonal streak between the fingers of a cactus plant, is seen in this time exposure, Nov. 18, 2001, in Tucson, Ariz. The Leonids are minute dust particles shed by Comet Tempel-Tuttle. (Arizona Daily Star/James S. Wood/Associated Press)

You can forget about ordinary fireworks this weekend. The heavens are going to put on a better show. In fact, the Royal Astronomical Society of Canada says this will be one of the better years for the annual Perseid meteor shower that lights up the summer sky.

It is predicting as many as 100 meteors an hour will streak across the sky on Sunday, August 12, the culmination of a celestial show that began on July 17. Although these fragments of comets should be visible most nights at this time of year, astronomers recommend hauling yourself outside sometime after 11 p.m. on Sunday if you want to see the passing parade at its peak.

Since it will also be a moonless night, it's a perfect time to comet-watch. But don't wait until next year: the British Astronomical Association says strong moonlight will make it difficult to see the Perseids in 2008.

What's a meteor shower?

A meteor streaks through the Hong Kong sky in this five-minute time exposure, Nov. 17, 1998. The celestial fireworks were actually particles in a long tail of the comet Tempel-Tuttle striking the atmosphere. (Associated Press)

Basically, it's composed of small particles of comets that break off as the comet travels through space and nears the sun. When these comet fragments enter the heavier atmosphere of Earth, they burn up because of friction and can glow for several seconds, lighting up the night sky.

The Perseid meteor storm is visible in Canada each year by mid-July, but most of the activity comes between Aug. 8 and Aug. 14. The Leonids are visible every year around mid-November.

Many people call these celestial fireworks "shooting stars," but they really don't have anything to do with stars at all.

A meteor is simply the name for a meteoroid — a piece of space rock or comet fragment — as it hits the Earth's atmosphere and burns up. It is usually pretty small.

If a part of the meteor survives the trip through the atmosphere and hits the ground, it's a meteorite. But that is a rare occurrence.

According to NASA, most meteors range in size from one millimetre to one centimetre in diameter, barely more than a grain of sand. The light they produce while burning up, however, is very intense and can be seen from hundreds of kilometres away.

Why are they called 'Leonids' or 'Perseids'?

The debris from a comet travels in parallel lines, and when that hits the Earth's atmosphere, it appears to originate from a single point, just as parallel train tracks appear to converge to a single point. The Leonids appear to be coming from the constellation Leo and the Perseids from the constellation Perseus, hence their names.

In reality, these showers occur when the Earth passes through the debris fields left mostly by specific comets. In July and August, it's debris from 109P/Swift-Tuttle we see. And every November, Earth passes through the debris field left by comet 55P/Tempel-Tuttle.

Leonids hit the Earth's atmosphere at 71 kilometres per second, or 255,600 km/h. That's about 133 times faster than an F-18 fighter jet can fly at top speed. If the meteor is extremely large and relatively near, it is possible to hear a distant rumble, or sonic boom created by the speed of the meteor.

Why are they so bright?

A Perseid meteor flashes across the sky on Aug. 12, 1997, in this eight-minute exposure taken in Florence Junction, Ariz. (SkyandTelescope.com, Rick Scott and Joe Orman/Associated Press)

The intense light of a meteor breaking up is created when a dust particle hits air molecules in the Earth's atmosphere. The impact vaporizes the outer layers of the meteor, leaving a trail of iron, magnesium and sodium.

When this trail of molecules makes subsequent impact with air molecules, the electrons are "bashed" out of their regular orbit with their corresponding nuclei, creating light in the process.

The colour of light produced depends upon the composition of the meteorite. Iron particles produce yellow light; sodium particles produce orange-yellow light; magnesium produces a blue-green light and silicon atoms produce red light.

Where to watch them

Find the darkest spot you can, away from light pollution. Try to get outside any settled area. In years where there is a bright moon, try to position yourself so its light is shielded from your field of vision.

North Americans will get an especially good view of the Perseids as the meteor shower is mostly limited to the Northern hemisphere.

Persieds can appear anywhere in the night sky and they are safe to watch with the naked eye. But they seem to emanate from the northeast quadrant because that is where the constellation Perseus is located.