Ready for summer’s and arguably the year’s best meteor shower? I see your fists pumping, so let’s get to it. Every August for at least the past 2000 years, Earth has passed through the debris trail left behind by Comet Swift-Tuttle. The comet, which takes 130 years to orbit around the sun, was discovered by independently by American astronomers Lewis Swift and Horace Tuttle in 1862.
Comets are like asteroids but composed primarily of ice and dust instead of rock. As a comet approaches the inner solar system, the sun’s heat vaporizes some of the dust-loaded ice and pushes it back to form a tail. Bits of solid material — fluffy dust, small clods and even fragments of ice — trail behind the comet.
Now the beauty part. If the comet’s orbit (trail) intersects that of Earth, we plow right into the debris over a period of several nights. You may find this unbelievable, but a Perseid meteor hits the thin air 50-75 miles overhead at speeds of around 134,000 miles per hour. At that speed, little bits of Swift-Tuttle vaporize in a flash of light making us shout at the sight. Because they’re moving so fast and the materials are generally small, almost all meteor shower meteors burn up completely. Not a single Perseid meteorite that we know of has ever been found.
The Perseid Meteor Shower is one of the most reliable with rates of around 60 meteors per hour visible from a dark sky site. If you’re closer to town, divide that number in half. My own notes over the years peg a good shower at around 40, but I’m sure I could do better if I wasn’t distracted with photography and telescope observing. Much of course depends on whether the moon is out or not. A bright moon during last year’s Perseids drowned out many of the fainter shooting stars. This year is different. The moon’s a crescent and sets well before midnight. Dark skies have many sky watchers feeling optimistic for a great show provided the weather’s friendly.
Nothing could be easier than watching a meteor shower. The radiant or point in the sky from which the meteors will appear to originate, is located in Perseus the Hero immediately below the W of Cassiopeia. During the early evening hours, the radiant is low in the northeastern sky. While you’ll see a modest number of meteors at the onset of night, the later you stay up, the higher the radiant rises, and the more meteors you’ll see all over the sky. Maximum activity occurs during early morning hours on Friday. To catch the show, all you need are your naked, eager eyes and a willingness to stay up later than your normal bedtime. Or you could go to bed early and set your alarm for around 2-3 a.m. to catch the peak. I usually mix it up, staying out for an hour in the evening and then waking up again in the wee hours.
The Perseids get their name because they appear to radiate from the constellation Perseus near Cassiopeia. Created with Stellarium
There are a few pieces of additional gear I’d recommend to enhance your sky watching experience. I like to wear a light coat and either kick back in one of those folding lawn chairs or flop out on a sleeping bag. Watching with a friend or family member not only keeps you awake but makes the event more fun as you listen to each other’s reactions. Sometimes a sports-style commentary develops regarding the performance of each meteor and its chances of making it into the night’s Top Ten.
You can look in any direction, but I prefer east to southeast with the radiant off to one side. Meteors near the radiant leave very short trails; those farther away are longer and more dramatic. Perseids are known for leaving bright, white “trains” or smoke trails in their wake. They travel so swiftly they ionize the surrounding air causing it to glow in a similar manner to a neon light sign. Trains can persist from a couple to many seconds, long after the meteor has disappeared. I once watched a Leonid meteor train get twisted into weird shapes by upper atmospheric winds for well over a minute.
Although railroad tracks are parallel to one another, they appear to merge in the distance in our eyes. Perseid meteors strike the atmosphere on similar parallel paths, but our perspective makes them appear to radiate from a point in the sky.
Any given night, some seven meteors an hour blaze randomly across the sky. Perseids are distinguished by their paths. Trace a meteor’s path backwards and if it takes you in the direction of Cassiopeia, it’s almost certainly a Perseid. Meteors originating from other directions are called sporadics and are unrelated to Comet Swift-Tuttle.
If you want to try some photography, attach your camera to a tripod, open the lens up to its widest aperture, and make time exposures of the sky from one to 5 minutes. If you keep at it, you’ll probably get portraits of at least a couple meteors. Last year I snagged one meteor for every 40 frames I took.
A meteor shower brings us face to face with fragments of our solar system’s icy wanderers, each mote an opportunity to wish upon a star. Here’s hoping clear skies visit you this week.