Get ready for what could be the most fantastic meteor display of the year. Every mid-August, Earth barrels through the trail of dusty crumbs left behind by Comet 109P/Swift-Tuttle. They strike our atmosphere at 67,000 mph (30 km/sec) and vaporize in flashes of light called meteors. Since they appear to radiate from a point in the sky in the constellation Perseus, they’re called the Perseids, one of a half-dozen major meteor showers each year.
Perseid meteor appear to radiate from a point in the constellation Perseus the Hero. The meteors arrive on parallel path as Earth passes through the swarm, but appear to converge in the distance the same way parallel railroad tracks do. It’s an illusion of perspective.
Typically the Perseids produce somewhere between 60-100 meteors per hour from a dark sky site, but this year’s shower comes with a twist that may double that number. Jupiter has gotten into the act according to meteor researcher Esko Lyytinen of Finland and Tom Van Flandern of the U.S. Naval Observatory. Every time the planet orbits the sun, it passes under the meteor stream and nudges a portion of the debris closer to Earth’s orbit. If Earth happens to encounter that denser pocket of material when we cross the Perseid stream in August, we get a boost in meteor sightings like we did in 2004 and 1980.
Russian meteor expert Mikhail Maslov predicts a maximum rate of 150-160 per hour from a very dark, moonless sky with the radiant high overhead. Maximum is expected about a couple hours after sunrise (7:40 a.m. CDT, 12:40 UT) Friday morning August 12, but since peak activity lasts for some 24 hours, expect to see more meteors than usual during this shower no matter where you live. Another strand of comet debris dating back to the year 1079 may provide an additional bump in numbers for U.S. observers, while two additional fresh “drops” from 1479 and 1862 will favor observers in Eastern Europe, the Middle East and western Asia during the overnight August 11-12.
On Thursday evening, you might see one meteor every couple minutes with the number rising toward dawn to perhaps two a minute. Evening sky watchers are more likely to spot Earthgrazers, Perseids that clip the top of the atmosphere and last many seconds before finally burning out. I like to set up my lawn chair facing east (in the evening) or southeast (in the morning), sit back just let them come. Since meteors typically flare about 60 miles high, if you gaze about halfway between the horizon and overhead point, your line of sight will put you in their sweet spot.
Perseids are generally white, fairly swift and often leave ‘trains’ or streaks of glowing light that linger a second before fading away. Watch for fireballs, too! The shower is no stranger to these brilliant meteors that can flare as bright as Venus or better.
The moon, one day past first quarter, will hinder the view only a little in the early evening, but it sets around 12:30 a.m., leaving the morning clear for the best part of the show. Sporadic meteors, unrelated to the Perseids, can appear from anywhere in the sky and provide a backdrop of 5-10 meteors per hour on any night you might go out. You’ll always know a sporadic from a true Perseid by tracing its trail backwards. If it points back to the radiant in Perseus, you just witnessed Comet Swift-Tuttle write its name across the sky.
Written by Bob King as published on The Astro Bob Blog