for National Geographic News
(Related: "Comet Swarm Delivered Earth's Oceans?")
Perseids start streaking across the sky as early as July and continue through late August. But the meteors usually peak in mid-August, with average rates of 70 to 80 shooting stars an hour.
Powerful Perseids This Year
This year's Perseids are even showier than normal, with an expected peak rate of a hundred meteors an hour.
Tuesday night through Wednesday dawn offered viewers the best chance to see the most Perseids without as much glare from the waning gibbous—or just past full—moon. (Take a moon facts quiz.)
But the actual peak of this year's Perseids is occuring this afternoon for people in North America. Although the meteors are essentially invisible in daylight, tonight's show could be just as plentiful, if not better.
After tonight, though, the numbers of shooting stars should taper off, with a rare bright streak appearing only occasionally.
This year's high number of Perseids is most likely a "gift" from the gas giant Saturn, said Bill Cooke of NASA's Meteoroid Environment Office in Huntsville, Alabama.
As Swift-Tuttle passes by the sun, the comet leaves debris strung out all along its orbital path through the solar system.
Over time, other forces have acted on those particles. Some have drifted apart, creating a spread that delivers a more consistent shower on Earth.
But Cooke thinks that at some point hundreds of years ago, the comet passed especially close to Saturn, and the pull of that planet's gravity helped concentrate nearby debris into a clump.
This year is special, Cooke said, because we're now passing through the debris herded together by Saturn, and "that clump of particles will encounter Earth only once."
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