Every August, the night sky is peppered with little bits of comet debris in what we call the annual Perseid meteor shower.
In 2018, the Perseids will peak on Aug. 12 (best showing the nights of Aug. 11-12 and Aug. 12-13), with 60-70 meteors per hour possible for observers with clear, dark skies, according to NASA.
The Perseids are bits of the comet Swift-Tuttle and often create the most amazing meteor shower of the year, although this year its splendor will be dampened slightly by a bright moon.
Comet Swift-Tuttle, whose debris creates the Perseids, is the largest object known to make repeated passes near Earth. Its nucleus is about 16 miles (26 kilometers) across, roughly equal to the object that wiped out the dinosaurs.
Back in the early 1990s, astronomer Brian Marsden calculated that Swift-Tuttle might actually hit Earth on a future pass. More observations quickly eliminated all possibility of a collision.
Marsden found, however, that the comet and Earth might experience a cosmic near miss (about a million miles) in 3044.
When a Perseid particle enters the atmosphere, it compresses the air in front of it, which heats up. The meteor, in turn, can be heated to more than 3,000 degrees Fahrenheit (1,650 Celsius).
The intense heat vaporizes most meteors, creating what we call shooting stars. Most become visible at around 60 miles up (97 kilometers).
Some large meteors splatter, causing a brighter flash called a fireball, and sometimes an explosion that can often be heard from the ground.
Lots of Comets
Comet Swift-Tuttle has many comet kin. Most originate in the distant Oort cloud, which extends nearly halfway to the next star. The vast majority never visit the inner solar system.
But a few, like Swift-Tuttle, have been gravitationally booted onto new trajectories, possibly by the gravity of a passing star long ago.
Perseid meteoroids are anywhere from 60 to 100 miles apart, even at the densest part of the river of debris left behind by comet Swift-Tuttle.
That river, in fact, is more like many streams, each deposited during a different pass of the comet on its 130-year orbit around the Sun.
The material drifts through space and, in fact, orbits the Sun on roughly the same path as the comet while also spreading out over time.
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