Tonight is the prime viewing window for this year's episode of the long-running Perseid meteor shower.

At least 50 or more meteors per hour, almost one per minute, can be expected to illuminate the night and early morning sky during the annual astronomical phenomenon.

As many as 100 meteors per hour may be attainable by viewing in locations away from strong city lights in predawn hours.

The tiny specks of cosmic rock and dust that become Perseid meteors hit our planet's atmosphere as the Earth circles the sun and passes through the orbital debris field left by the comet Swift-Tuttle during its 133-year circuit through our solar system.

The meteors slam into our upper atmosphere at about 210,000 kilometres per hour and vaporize 100 kilometres above us with an average heat of 1,600° C, creating a sometimes colourful and lasting ionized gas trail that arcs across the night canopy.

The Perseids have the distinction of featuring more spectacular "fireballs" than any other yearly meteor shower.

This year's peak viewing nights are August 11, 12, and 13, but the shower will remain active, with gradually decreasing hourly numbers, until August 26. The light of the waning moon, which will be about 47 percent full, might interfere with viewing some of the fainter meteors, but most should still be visible, especially if you head out to watch before moonrise. (After August 17, the moon's interference will have virtually disappeared.)

Best viewing hours are generally between midnight and dawn. The Perseids' "radiant point", or the spot in the night sky from where the meteors appear to originate, is in the constellation Perseus, which will be highest in the Northern Hemisphere night sky just before dawn.

Fireballs are larger than usual and exceptionally bright meteors that leave longer and persisting trails, often featuring different colours—depending on the individual meteor's mineral content—as they vaporize.

Meteor expert Bill Cooke, who heads up NASA's Meteoroid Environment Office, calls this popular annual display of celestial fireworks the "fireball champion" of all meteor showers.

"We have found that one meteor shower produces more fireballs than any other," Cooke said on the NASA Science website's Perseids page. "It's the Perseid meteor shower, which peaks on August 12 and 13."

Cooke, who reached this conclusion after analyzing 12 years' worth of data collected from a network of meteor cameras across the U.S., says the relatively large number of Perseid fireballs probably stems from the size of the parent comet.

"Comet Swift-Tuttle has a huge nucleus—about 26 kilometres in diameter," Cooke says. "Most other comets are much smaller, with nuclei only a few kilometers across. As a result, Comet Swift-Tuttle produces a large number of meteoroids, many of which are large enough to produce fireballs."

Head out to view the Perseids, preferably away from strong city lights, between 10:30 p.m. and 4:30 a.m. The peak number of meteors will be closer to the predawn hours, but there will be plenty available for viewing before then, depending on local weather conditions. (Vancouver's skies are expected to be partly cloudy tonight [August 12], with clear skies predicted for the next few nights.)