Shooting stars

Have you ever seen a quick flash of light race across the night sky? That was a meteor. Let's find out what is really happening up there.

Not stars at all

A shooting star looks like a star that has come loose and dashed across the sky. But real stars are enormous balls of hot gas, very far away, and they do not fall. A shooting star is actually a meteor.

Most meteors are made by meteoroids no bigger than a grain of sand. They hit the air around Earth at astonishing speeds, somewhere between about 11 and 72 kilometres every second. That is far faster than a rocket. As the tiny grain rushes into the air, it squashes and heats the air in front of it so much that the air glows. At the same time the grain itself burns away. All of this happens high above the clouds, roughly 80 to 120 kilometres up.

Over in a flash

Most meteors last less than a second. Blink and you will miss them! Some are faint and white. Others can look yellow, orange, green or blue, depending on what the grain is made of and how fast it is going.

On a clear, dark night, away from street lights, you can usually spot a few meteors every hour on any night of the year. These are called sporadic meteors, because they turn up at random.

Occasionally a bigger meteoroid makes a much brighter meteor called a fireball. A fireball can be brighter than the planet Venus, and very big ones can even light up the ground. Fireballs are rare, but cameras around the world watch the sky every night to catch them.

Meteor showers

At certain times of year, Earth passes through trails of dust left behind by comets. Comets are icy balls of dust and frozen gases that travel around the Sun. As a comet warms up near the Sun, it sheds dust along its path.

When Earth ploughs through one of these dusty trails, we see many more meteors than usual. This is called a meteor shower. All the meteors in a shower seem to come from the same small patch of sky, and the shower is named after the constellation in that patch. The Perseids, in August, seem to come from the constellation Perseus. The Geminids, in December, seem to come from Gemini.

The grains in meteor showers are so small and crumbly that they burn up completely, so showers do not drop meteorites.

Did you know?