Spectacular "outburst" of Perseid meteors expected tonight

Astronomers are predicting dazzling pyrotechnics in the predawn skies over the Northern Hemisphere tonight as the Perseid meteor shower is expected to showcase one of its periodic "outburst" years.

The annual display of streaking meteors is caused by the Earth moving through cosmic debris left by the regular passage of the Swift-Tuttle comet in our solar system and lasts about a month, but the most spectacular shows come in irregular cycles. 

Scientists using computer programs have determined that the comet's orbit sometimes results in its ejected dust and rock particles being compressed by the gravitational forces exerted by our system's giant planets, especially Jupiter. This clumping then leads to a sky watcher's delight of 150 to 200 visible meteor streaks per hour—including occasional "fireballs"—up from the more usual 80 per hour.

The viewing is best after midnight, preferably in a cloudless sky and from outside large cities, to reduce light pollution that restricts visibility. If you are in the city, try to get to a large playing field or park and allow for at least 45 minutes for your eyes to adjust to the night sky.

The most rewarding spectator results in the Lower Mainland should come well after midnight (although some bright streaks should be periodically visible as early as 10 p.m.), with the meteors appearing to radiate from the northeast, where the constellation Perseus will appear late at night. Meteors will be visible in the following days, but the peak is expected to happen the night of August 11-12, with the time around 3 a.m. rewarding the most devoted of night owls.

Astronomers note that moonfall will also increase the visibility of the meteors, which are usually not much bigger than a grain of sand but which burn in a fiery, glowing burst as they hit Earth's atmosphere.