A perennial favorite among skywatchers, the Perseid meteor shower makes its annual return on the nights of August 11-12 and 12-13.The Perseid meteor shower peaks this year when there's almost no Moon, affording a dark sky for late-night shooting-star spectators and counters. A thick waxing crescent Moon sets in mid-evening, so it will offer little interference for this year's event.
Earth should go through the densest part of the stream for some hours on August 12th around 19h Universal Time, which is 3 p.m. Eastern Daylight Time. This means the shower's peak splits the difference between the early-morning hours of August 12th and 13th for anyone in North America or Europe. So the number you count on each of those mornings, even in ideal conditions (no light pollution and the radiant nearly overhead) might not match the International Meteor Organization's predicted peak of 100 per hour. But surprises can always happen.Some Perseids appear beginning around 9 p.m., but they're always better from about 11 p.m. or midnight until the first light of dawn. This is when the shower's radiant point in northern Perseus climbs high in the northeastern sky. Or, to put it another way, this is when your side of Earth turns to face the oncoming meteor stream more directly.
These "shooting stars" are actually bits of debris shed by Comet 109P/Swift-Tuttle. Streaking into Earth's upper atmosphere at a relatively fast 37 miles (60 km) per second, they create superheated plasma (ionized air molecules) along their path. This incandescent gas, which includes vapor from the incinerating particle, creates the momentary streaks of light we see in the sky.Bigger particles create bigger flashes, called fireballs. Using a network of meteor cameras distributed across the southern U.S., a team of NASA scientists has amassed a database of hundreds of very bright meteors since 2008. They've found that the Perseids are richer in these showy flashes than any other shower.
Moreover, notes William Cooke of NASA's Marshall Space Flight Center, the average bright Perseid in the census has a magnitude of –2.7, compared with –2.0 for the Geminids. (A fireball is any meteor of –4 or brighter.)
"Comet Swift-Tuttle has a huge nucleus — about 26 km [16 miles] in diameter," explains Cooke. "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."
Two much weaker showers are also active at this time of year, the Delta Aquariids and Kappa Cygnids.Meteor-watching is easy! Find a spot with an open sky view and no bright lights. Lie back in a reclining lawn chair, bundle up in a sleeping bag against mosquitoes and the late-night cold, and watch the stars. Expect an average of roughly one Perseid per minute under fine conditions, fewer of them if you have significant light pollution.
Check out these helpful tips for enhancing your Perseid watch. Try making a reportable meteor count, using the methods detailed by the IMO. Send your observations to the IMO or to the North American Meteor Network. And watch other observers' counts accumulate almost in real time.
The Perseids were especially dramatic in the 1990s around the time of Swift-Tuttle's most recent return, but they have since reverted to normal. The comet isn't due back until around 2122.
For more on meteor-watching, download our new ebook, Shooting Stars. It's free!
And for a laugh, check out XKCD's tongue-in-cheek guide to this year's meteor showers.