Dark Nights for the Perseids

GainLee recorded this montage of bright Perseids over a two-hour period inAugust 2007 from his heavily light-polluted backyard in Huddersfield,England. He took many short exposures with a 15-mm f/2.8 fisheye lens,then combined the lucky few frames that captured a meteor with one thatincluded the foreground. Click herefor a wider view, which shows Cassiopeia near center and the shower'sradiant point below it in northern Perseus. The nonconformist meteor offby the Big Dipper at far left is a Kappa Cygnid.Gain LeeThe last time the annual Perseid meteor shower happened during arun of good moonless nights was in 2007. It turns out that every threeyears, the same phase of the Moon returns to roughly the same date eachmonth (2.2 days earlier, on average). So in 2010 we're on for moonlessPerseids again!

The shower lasts for many days, but according to the International Meteor Organization this year's peakshould occur during a half-day-long window centered on 1:00 UniversalTime on August 13th, which is ideal timing for skywatchers in Eurasia.For North Americans, the best viewing will probably be late Thursdaynight and early Friday morning, August 12-13, or possibly the nightbefore.

In any case, prime viewing for the Perseids is from about11 p.m. or midnight (local time) until the first light of dawn. This iswhen the shower's radiant (its perspective point of origin) is well up in your sky. The higher the radiant, the more meteors you'll see.

ThePerseid meteors appear to stream away from their radiant near theborder of Perseus and Cassiopeia. And while you're outside on a darknight, don't forget to look for the Double Cluster and the AndromedaGalaxy, two of the easiest "faint fuzzies" to spot with your unaidedeyes.S&T IllustrationMany longtime skywatchers remember the fine displays the Perseidsput on in the early 1990s, around when the shower's parent comet,109P/Swift-Tuttle, last passed through the inner solar system. Thosedays are gone; the comet won't be back until 2126. But even now some,thin, dense filaments of meteoroids that the comet shed in recentcenturies continue to liven up the shower's behavior. Strands leftbehind by the comet in 441 and 1479 might be in play this year, thoughonly a little enhancement is expected from them.

At a very dark,rural site, you can probably expect to see 100 or more meteors per hourwhen the radiant (in northern Perseus) is highest in your sky before thefirst light of dawn. Any light pollution will cut down on the numbers,as will the radiant's lower altitude earlier in the night. But thebrightest few meteors shine right through light pollution, and the fewthat happen when the radiant is low are especially long, skimming theupper atmosphere and flying far across the sky.

To get the mostenjoyment while watching for Perseids, find a dark spot with an open skyview, bundle up thoroughly in blankets or a sleeping bag (for mosquitoshielding as well as warmth, and don't forget the repellent), and lieback in a reclining chair. Gaze into the stars, and be patient. The bestdirection to watch is wherever your sky is darkest, usually straightup, perhaps with a little inclination toward the radiant. That's allthere is to it!

In2009 the Perseid shower displayed three separate, strong peaks duringits most active 36 hours (shown in Universal Time), as revealed in thisplot based on 8,158 Perseid sightings reported by 144 observersworldwide.Geert Barentsen / IMOIf you're a little more ambitious, you can make a careful meteor count and report it to the International Meteor Organization. Such counts are analyzed to yield the shower's zenithal hourly rate,which is the number of meteors that a single observer would see perhour under ideal conditions: with the radiant directly overhead (at thezenith) and the sky dark enough to reveal 6.5-magnitude stars.

Notall the meteors you'll see are Perseids. In addition to occasionalrandom, sporadic meteors, the weaker Delta Aquarid shower is also activeduring Perseid season. The Delta Aquarids are slower, often yellower,and track away from a radiant point in eastern Aquarius. Weaker stillare the Kappa Cygnids, identifiable by their flight direction away fromCygnus in an altogether different part of the sky.

Don't forgetthat the Perseid shower lasts for more than one night! Rates are about aquarter to half the peak for one or two nights before and after. A fewforerunners of the shower may show up as early as July 20th, andstragglers have been recorded as late as August 24th.

Posted by Alan MacRobert, July 27, 2010related content: Celestial events