When a bright streak of light flashes across the night sky, it is commonly referred to as a “shooting star.” Despite the name, this phenomenon has nothing to do with stars, which are distant suns. The light display is instead a highly visible scientific process involving tiny pieces of cosmic debris encountering Earth’s atmosphere at immense speeds.
Defining the Terminology
The object responsible for the light show is named based on its location in space. A piece of rocky or metallic debris orbiting the Sun is known as a meteoroid, ranging in size from a grain of sand up to a few meters wide.
When a meteoroid enters Earth’s atmosphere, it becomes a meteor. The meteor is not the solid object itself, but the visible streak of light caused by the meteoroid’s rapid entry and subsequent vaporization. This luminous trail is what the public calls a “shooting star.”
If the space rock is large enough to survive its fiery passage and reaches the Earth’s surface, it is classified as a meteorite. This change in terminology reflects the object’s survival status and its location relative to our planet.
The Source Material
The small particles that become meteors originate primarily from two types of parent bodies. Many meteoroids are fragments of ancient, larger asteroids orbiting the Sun, mainly in the asteroid belt between Mars and Jupiter.
Other meteoroids, particularly those responsible for predictable meteor showers, come from comets. As a comet orbits the Sun, its icy composition warms up and releases gas and dust, leaving behind a trail of debris. When Earth intersects one of these dusty trails, increased meteor activity occurs. The meteoroids that create visible streaks are often no larger than a grain of sand or a small pebble.
The Atmospheric Flash
The intense light of a shooting star is generated when a meteoroid plunges into Earth’s atmosphere at extreme velocities, typically ranging from 11 to 72 kilometers per second. At these speeds, the meteoroid compresses the air directly in front of it, creating a high-pressure shockwave.
This compression, rather than simple friction, causes the air molecules and the meteoroid’s surface to heat up rapidly. The resulting thermal energy causes the meteoroid’s material to vaporize and the surrounding atmospheric gases to become excited and ionized. This superheated, glowing material forms a plasma trail, which we perceive as the bright streak of a meteor.
Most disintegration occurs in the mesosphere, the layer of the atmosphere between roughly 75 and 120 kilometers above the surface. The vast majority of meteoroids are completely vaporized at altitudes between 50 and 95 kilometers, ensuring they never reach the ground.