Meteor

A meteor is the luminous phenomenon produced when a fragment of solid matter— a meteoroid—enters Earth’s atmosphere at high speed. Friction with the air heats the fragment and the surrounding gas to the point of ionization, creating a luminous trail that can last from a few fractions of a second to several seconds. Commonly called a shooting star, it has nothing to do with stars.

The mechanism of a meteor

When a meteoroid enters the atmosphere at speeds typically ranging from 11 to 72 kilometers per second, it compresses the air in front of it. This rapid compression heats the gas to temperatures exceeding 1,600 degrees Celsius, vaporizing the fragment and ionizing the air. It is this ionized air—not the fragment itself—that burns, producing most of the visible glow. The process generally occurs at altitudes between 80 and 120 kilometers.

Meteors and meteor showers

Isolated meteors, known as sporadic meteors, can occur at any time during the night. Meteor showers occur when Earth passes through the trail of debris left behind by a comet. These swarms of particles follow similar orbits and enter the atmosphere from the same direction, appearing to radiate from a single point in the sky— the radiant. The Perseids (August), the Leonids (November), and the Geminids (December) are among the best-known meteor showers.

Bolides and fireballs

Particularly bright meteors, with a magnitude greater than -3, are called bolides or fireballs. They can cast shadows on the ground, produce sonic booms, and sometimes send fragments to the ground in the form of meteorites. The 2013 Chelyabinsk fireball is the most recent and best-documented example.

Concrete example

The Geminids, active every December, are one of the most prolific meteor showers, with up to 120 meteors per hour at their peak. What makes them unique is that they originate not from a comet but from an asteroid— 3200 Phaethon — which remains an exception in the meteor shower calendar.

Frequently Asked Questions

Why do shooting stars appear to come from the same point?

It’s a perspective effect, like snowflakes that seem to come from the same point in front of a car. The particles in a meteor shower travel in parallel through space, but their projection onto the celestial sphere makes them appear to emanate from a single point— the radiant of the shower.

What is the difference between a meteor and a meteorite?

A meteor is the luminous phenomenon in the atmosphere. A meteorite is the solid fragment that reaches the ground after surviving its passage through the atmosphere. The vast majority of meteoroids burn up completely before reaching the ground.

Are meteors visible in broad daylight?

The brightest ones, known as fireballs, can be visible in broad daylight. A famous example is the fireball of June 30, 1908 (the Tunguska event), whose glow was seen hundreds of kilometers away in the middle of the morning.