The streaks of light briefly flashing across the night sky, commonly called “shooting stars,” are not stars at all. These phenomena are small pieces of space rock and debris encountering Earth’s atmosphere at high speeds. The scientific term for a “shooting star” is a meteor, which is the visible effect created when an object from space burns up high above the planet’s surface. Understanding this light requires distinguishing between a space rock’s location and its ultimate fate as it interacts with our atmosphere.
Defining the Cosmic Debris
The nomenclature for these celestial objects depends on their location relative to Earth’s atmosphere. A meteoroid is the initial object, a small piece of rock or metal traveling through space, ranging from a grain of dust up to about one meter in diameter. Most meteoroids that create visible streaks are small, often no larger than a grain of sand.
When a meteoroid enters the atmosphere, the intense heat and light transform it into a meteor, the visible streak or “shooting star.” The visible light is the luminous trail created as the object vaporizes and interacts with the air. If the object is large enough to survive this journey and land on the ground, the remnant is called a meteorite.
The Origin of the Material
The material that becomes a meteoroid originates primarily from two sources: comets and asteroids. The majority of meteors seen, particularly those in meteor showers, are fragments shed by comets. As a comet orbits the Sun, its ice vaporizes, releasing dust and rocky debris that form persistent trails in space.
Other meteoroids are fragments of asteroids, which are larger, rocky bodies orbiting the Sun, mostly located in the asteroid belt between Mars and Jupiter. Collisions or gravitational disturbances chip off smaller pieces that travel toward Earth. Earth regularly passes through these cometary debris streams, resulting in predictable annual events where many meteors appear to originate from the same point in the sky.
The Science Behind the Flash
The flash of light is caused by a rapid interaction between the space rock and the atmosphere, not by simple combustion. A meteoroid enters the atmosphere at extreme speeds. At these hyper-velocities, the air in front of the object is violently compressed, creating a superheated region known as a shock wave.
This compression, not friction, is the main source of the immense heat generated, quickly raising the temperature of the air molecules to thousands of degrees. The resulting thermal energy causes the air and the meteoroid’s surface layers to vaporize and ionize, forming a glowing plasma. This plasma produces the brilliant visible streak across the night sky. The different colors sometimes observed, such as green or red, result from specific elements in the meteoroid’s composition glowing at characteristic wavelengths.