What Are Shooting Stars? Meteors, Meteor Showers and Where to See Them

You are lying on the grass on a summer night when a thin streak of light flashes across the sky and vanishes in a second. In many cultures people make a wish. But what you just saw was not a star. It was a speck of dust, older than the Earth itself, dying in a flash high above your head.

Meteoroid, meteor, meteorite

The names can be confusing, so it helps to sort them out first:

• Meteoroid: a small piece of rock, metal or dust travelling through space.
• Meteor: the streak of light we see when a meteoroid enters the atmosphere. This is the “shooting star”.
• Meteorite: a piece that survives the fiery trip and lands on the ground.

Most meteors come from meteoroids that are astonishingly small, often no bigger than a grain of sand. They shine so brightly because of their speed, not their size.

Why does a speck of dust glow so brightly?

Meteoroids hit the atmosphere at between 11 and 72 kilometres per second, up to 200 times faster than a bullet. At the high end they would cross a big city in under a second.

At an altitude of about 80 to 120 kilometres, the air is thin, but not thin enough. The meteoroid slams into air molecules so hard that the air in front of it is squeezed and heated to thousands of degrees. Its surface melts and vaporises, a process called ablation, and the vaporised atoms and surrounding air are ionised and glow. Contrary to popular belief, this is not simple friction like rubbing your hands together; it is closer to the heating of air ahead of a re-entering spacecraft.

The colour of a meteor can hint at its chemistry. Sodium gives an orange-yellow glow, magnesium blue-green and calcium violet, while the heated nitrogen and oxygen in the air can add red.

Where do meteoroids come from?

Most meteoroids are crumbs from comets and asteroids. When a comet approaches the Sun, its ice turns to gas and releases dust and grit that spread along its orbit. Collisions between asteroids also chip off fragments.

On any clear night you can see a few random meteors per hour; astronomers call these sporadic meteors. But a few times a year, the numbers jump.

Why do meteor showers return every year?

A comet’s orbit is littered with a long, thin river of debris. Earth crosses some of these rivers at the same point in its own orbit each year, and so on the same dates. When it does, it sweeps up thousands of particles, and we get a meteor shower.

All the meteors in a shower travel in parallel. Like railway tracks seeming to meet in the distance, their paths appear to start from one point in the sky called the radiant. Showers are named after the constellation that contains it: the Perseids seem to come from Perseus, the Geminids from Gemini.

Some showers have famous parents. The Perseids come from Comet Swift–Tuttle, a mountain of ice about 26 km across. The Geminids are unusual because their parent, 3200 Phaethon, looks more like an asteroid than a comet.

Earth is gaining weight

All this dust adds up. Scientists who collected tiny micrometeorites from the clean snow of Dome C in Antarctica estimated that about 5,200 tonnes of extraterrestrial dust reach Earth’s surface each year. Most of it is too small to notice. Some of the dust on your windowsill may literally have come from space.

How to see more shooting stars

• Get away from lights. A dark sky can show ten times more meteors than a city.
• Wait until after midnight. In the early morning your side of Earth faces forward in its orbit, so it runs into more meteoroids, like a car windscreen in rain.
• Give your eyes time. It takes 20 to 30 minutes for your eyes to adapt fully to the dark. Avoid looking at your phone.
• Look at a wide patch of sky, not directly at the radiant. Meteors can appear anywhere.
• Check the Moon. A bright full Moon can hide most meteors.

In short

• A shooting star is a meteor: a tiny meteoroid burning up in the atmosphere, not a star.
• It glows at 80–120 km because it hits the air at 11–72 km per second, heating and ionising the air in front of it.
• Meteor showers happen when Earth crosses a comet’s debris trail on the same dates each year.
• The Perseids (August) and Geminids (December) are the strongest regular showers.
• Earth collects thousands of tonnes of space dust every year.