What a shooting star actually is

A shooting star isn't a star. It is a grain of dust from space, often smaller than a grain of sand, hitting Earth's air so fast that it heats up and glows for a second, 70 to 100 kilometers above the ground. Astronomers call the streak a meteor. Meteor showers happen on the same dates every year, because Earth crosses the same dust trails on the same days of its orbit.

Why such a small thing glows

Speed. Meteors hit the air at tens of kilometers a second: Geminids at about 35, Leonids at about 71, according to the American Meteor Society. At that speed the air in front of the grain is squeezed and heated so much that the grain burns away and the air around it glows. A grain the size of a sand grain can make a streak you see from a hundred kilometers away.

Why showers have dates

Comets shed dust as they go around the Sun, and the dust spreads out along the comet's path. Earth crosses some of those trails at the same point in its orbit every year, so the shower comes on the same dates: the Perseids every August, the Geminids every December.

Two famous showers come from asteroids instead: the Geminids from 3200 Phaethon and the Quadrantids from a small object called 2003 EH1. And Halley's Comet gives two showers a year, the Eta Aquariids in May and the Orionids in October.

Why they seem to come from one point

The grains in a shower travel side by side, like rain. When you drive through snow, the flakes seem to come from one point ahead of the car; meteor trails do the same, and that point is called the radiant. A shower is named for the constellation its radiant is in.

What reaches the ground

Almost nothing from a shower: shower grains are tiny and burn up completely. Bigger rocks, from asteroids, sometimes survive the trip and land; those are meteorites. They are rare, and most fall in the sea or in places nobody lives.

Seeing more of them

On any dark night, without a shower, a patient watcher sees a few meteors an hour: these are stray grains from no particular trail. On a good shower's peak night, the count goes up a lot. To see more, go somewhere dark, wait until the Moon is down, lie back to take in as much sky as possible and give your eyes twenty minutes. Every shower page on Peabody has the next peak night and a verdict on the Moon.

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“Read it, then go and look. The sky is the best page in the book.”