Streaks of light that flash briefly across the night sky often seem to come from a single source. This striking display is called a meteor shower, and far from being a random event, it's a predictable consequence of Earth passing through the same points in its orbit every year.
How Meteor Showers Form
When a comet approaches the Sun, the ice on its surface heats up and vaporizes, scattering tiny dust-sized particles into space. As the comet completes lap after lap around the Sun, these particles gradually spread into a wide trail of debris stretched along the comet's orbit. As Earth moves along its own orbit, it passes through these debris trails at certain times each year; the particles inside them slam into the atmosphere at tens of kilometers per second, heat up from friction, and burn up in brief streaks of light — what we call "shooting stars." Most of these particles range from the size of a grain of sand to a pea, and nearly all of them burn up completely before ever reaching the ground.
Why the Radiant Point Matters
During a meteor shower, the paths of the falling meteors appear to spread out from a single point in the sky, known as the radiant point. This is the same kind of perspective illusion that makes parallel train tracks appear to converge in the distance: the particles are actually traveling along parallel paths, but to an observer they appear to fan out from one spot. Showers are usually named after the constellation where this radiant point sits — a shower whose radiant lies in Perseus, for instance, is called the Perseids.
Well-Known Showers and Their Cometary Origins
Every meteor shower has a specific parent comet (or, occasionally, an asteroid) behind it. The Perseids, which peak in mid-August and rank among the year's most reliable showers, come from the trail left by comet 109P/Swift-Tuttle, which orbits the Sun once every 133 years. The Leonids in November trace back to comet Tempel-Tuttle, while the October Orionids and the May Eta Aquariids are both linked to the famous Halley's Comet. December's Geminids, often considered one of the year's brightest showers, are a notable exception: their source isn't a comet at all, but an asteroid called 3200 Phaethon.
What Determines How Intense a Shower Will Be
How strong a shower appears depends on whether Earth passes through the densest part of a debris trail or just grazes its edge. Because the particles in a comet's trail disperse gradually over time, some years bring a sparser display, while in others — when Earth crosses a particularly dense stretch — observers can witness "meteor storms" with hundreds of meteors per hour. The Moon's brightness that night, light pollution at the observer's location, and how high the radiant point sits above the horizon also directly affect how many meteors are visible.
Tips for Watching
No special equipment is needed to watch a meteor shower — just a dark spot with a wide view of the sky and the naked eye. Since it can take 20 to 30 minutes for your eyes to adjust to the dark, it helps to avoid looking at a phone screen during that time. For most showers, the best viewing window is in the hours after midnight, once the radiant point has risen higher in the sky.