For the next week, Colorado’s night skies will be full of shooting stars. Despite the name, they aren’t actually stars — they’re space debris, and they’re part of the annual Perseid meteor shower.
Tiny but bright comet debris
Meteor showers occur when the Earth passes through dust and rock in space. Most of the time, those particles burn up as they speed through our atmosphere. They get so hot on the descent that they glow, creating the well-known streaks of light in the night sky.
John Keller, director of Fiske Planetarium at the University of Colorado Boulder, said the meteors are only 50 to 100 miles above the ground, but they’re usually fairly small.
“Even though these streaks look really bright, they’re really grains of dust sized, they’re grains of sand sized. There can be larger chunks, that are pebble-sized or marble-sized or gravel-sized,” he said. “But it doesn’t take a whole bunch of mass going that fast to make a really bright light.”
The terms for each of these pieces of debris depend on where they are on their journey to Earth.
“A meteoroid is something that is going to smash into the Earth. As it’s coming towards the Earth, it’s called a meteor. And if it lands, it’s a meteorite,” said Keller. “So they all have meteor in them, but meteoroids, meteors and meteorites are the three phases of almost hitting the atmosphere, hitting the atmosphere, and then making it through the atmosphere.”
The dust and rock can come from multiple sources. Asteroids can collide together in the asteroid belt between Mars and Jupiter and shoot chunks of rock towards Earth, but that usually only results in a couple of meteors. The meteors from asteroids are generally larger, so more meteorites make it to the ground.
A full-blown meteor shower requires more dust. Keller said in that case, the Earth is passing through debris from a comet. During the Perseids, it’s comet Swift-Tuttle.
“You’re going to have literally like 60 of these (meteors) coming through the atmosphere every hour because there’s a lot of dust that was left over by that comet,” he said.
Comets are big dirty snowballs on long orbits. They only come close to the Sun every few hundred years, but they are constantly losing and leaving behind a trail of material.
“When it is in the proximity of the inner solar system, that’s when it heats up because it’s closest to the sun. That heat sublimates the ice and releases both ice and dust. The ice goes away as gas, but the dust remains,” said Keller. “That dust actually follows the same orbital trajectory. It actually continues going around in space.”
The dust keeps orbiting around the Sun in the same path as the comet, even after it gets pulled off the comet. Swift-Tuttle has been orbiting the Sun for millions of years, which means there’s always material for the Earth to collide with in August, the time of year when the Earth’s orbit intersects the orbiting dust.
The strength of the meteor shower can change each year because the comet leaves behind varying amounts of dust.
Viewing the Perseids
While the comet creating this astronomical event is called Swift-Tuttle, the meteor shower itself is named after a constellation.
“They’re called the Perseids because actually every meteor shower is named off of the constellation where it looks like the meteors are coming from. This is called the radiant,” said Keller. “In the case of the Perseids, the radiant is the constellation of Perseus.”
He compared it to driving at night during a blizzard.
“The Earth is the car. The atmosphere is the windshield. We’re driving our atmosphere with the windshield into a snowstorm, which is the dust that we are going to impact,” he said. “And it all looks like it’s coming from the direction we’re travelling.”
Try to get as wide a view of the sky as possible, preferably in a dark location.
Because the Earth is moving towards the constellation of Perseus when we run into the comet debris, it looks like all of the meteors are coming from that area of the sky.
But Keller said just staring straight at Perseus isn’t the best strategy for viewing the meteors. Instead, try to get as wide a view of the sky as possible, preferably in a dark location. And this year, the moon won’t be a problem.
“We’re really lucky this year in that the moon is actually going to be a waxing crescent, which means it will be just past being a new moon,” he said. “It’s only going to be 13% illuminated, so not super bright in the sky. And it’s also going to set very early.”
The Perseids last from mid-July to late August. The peak is the night of Aug. 11 and morning of Aug. 12.
There will be a lot of meteors all night long, but Keller said the most will come in the morning hours, after midnight. He recommended lying on your back to take in as much of the experience as possible.
