Stargazing in the Big Sky

Perseid meteor shower

By Ashley Oliverio EBS Contributor

The nights of Aug. 12-14 bring the peak of the annual Perseid – pronounced “PER-see-id” – meteor shower. Occurring during the summer’s warm weather, the Perseids are the most widely observed meteor display of the year.

Named for the constellation Perseus, the location in the sky where the “shooting stars” all seem to emanate, the Perseids originate from dust, ice and rock left in the wake of Comet 109P/Swift-Tuttle. The comet passes through our inner solar system every 133 years, and its last flyby occurred in 1992. Each year from about mid-July to late August, Earth slams into Swift-Tuttle’s castoff debris stream.

On the mornings of Aug. 12 and 13, we will hit the dense center of the comet’s rocky path, and watchers under dark skies will likely count up to 100 meteors per hour from midnight to dawn. If staying up late or rising early is unappealing, take heart: Perseids will appear starting about 10 p.m. as their common starting point, or radiant, in Perseus rises over the northeastern horizon.

Moonlight will not interfere with the Perseids this year. The moon will be near its new phase, rising and setting with the sun, during the apex.

To successfully observe the Perseids, go to a site free of manmade lights. Bring a coat and blanket, bug repellent, snacks, plenty of warm beverages and a lawn chair for comfortable sky gazing. And don’t forget your friends and family! Telescopes and binoculars are unnecessary: Since the Perseids zip across the sky so swiftly and soar in all directions, your eye’s naturally wide field of view is best.

While they bear a constellation’s name, the Perseids have nothing to do with the distant suns that form the star pattern Perseus. Comet Swift-Tuttle’s jettisoned rubble lies close to Earth and encounters us from the general direction of the sky where the stars of Perseus are found twinkling trillions of miles away.

We see the Perseids spray out of Perseus just like you’d see snowflakes fly at you from a seemingly common point beyond your car windshield, as you drive through a blizzard.

The “falling stars” we glimpse during a meteor display might seem huge and close to the ground, but this is an optical illusion. Most meteors are caused by tiny comet and asteroid particles burning up high in our atmosphere.

The impact speed of those little shards produces tremendous power: The frozen, stony detritus that creates the Perseids crashes into Earth’s atmosphere at 37 miles per second – or more than 130,000 mph – making this one of the fastest of all meteor showers.

At this impact speed, the Perseid particles heat up and fry approximately 60 miles above us, with dazzling glowing streaks marking their flight paths. Also, due to the Perseids’ velocity, these meteors often manifest with exceptionally bright, long flashes before dissolving into darkness. This spectacle is also an illusion: A Perseid meteor trail is typically only about 1 yard wide, but tens of miles long.

While the earliest record of Perseid activity comes from the Chinese in A.D. 36, a more familiar reference to them is found in John Denver’s hit song “Rocky Mountain High.” While composing a new album, the then 27-year-old musician observed the Perseids from a lake near Aspen, Colo. The meteor display that August night inspired him to write the lyrics “I’ve seen it raining fire in the sky.”

If we get cloudless nights, hopefully we will all see it rain fire in Big Sky during this event.

Ashley Oliverio recently moved to Big Sky and was the former president of the Helena Astronomical Society, and head of public relations and communication for Carroll College. She has more than 20 years of experience as a writer, editor and astronomy columnist for Helena newspapers.