A meteor is the visible or otherwise detectable atmospheric phenomenon produced when a meteoroid or related fragment enters a planetary atmosphere at high speed and interacts with atmospheric gases. The light is produced mainly by heating, excitation and ionisation of atmospheric and meteoroid material, combined with radiation from the hot ablated material. The term meteor therefore refers to an event or phenomenon rather than the solid object itself.
The solid object in space is a meteoroid, while a surviving piece that reaches the ground is a meteorite. Meteors are commonly called shooting stars or falling stars in everyday language, but they are not stars and are not physically related to stellar objects. Earth's atmosphere produces many meteors every day, most of them far too faint to be noticed without sensitive instruments. The brightest events can become fireballs or bolides and may sometimes be associated with meteorite falls.
A meteor begins when a meteoroid encounters an atmosphere at high velocity. Typical atmospheric entry speeds for meteoroids around Earth range from roughly eleven kilometres per second to more than seventy kilometres per second, depending on the object's heliocentric orbit and the geometry of its encounter with Earth. As the object descends, atmospheric molecules collide with its leading surface at enormous relative speeds. The resulting compression and heating generate a luminous region around the body.
Material is progressively removed through ablation, and the object's kinetic energy is converted into heat, light, ionisation, fragmentation and atmospheric motion. The brightness depends on the object's mass, velocity, composition, shape and fragmentation behaviour. A small meteoroid may produce only a brief faint streak, whereas a larger object can generate a brilliant fireball visible across a large area.
The visible trail of a meteor is not simply a glowing rock travelling through empty air. The atmosphere becomes ionised along the object's path, producing a plasma trail containing charged particles and excited atoms and molecules. Some meteor trails can persist visually for a short period, particularly when atmospheric winds and turbulence shape the ionised material. Radar can detect these trails even when the meteor itself is not visually bright.
The emitted light includes contributions from excited atmospheric species and vapourised meteoroid material. Spectroscopy can reveal information about the chemical composition of the meteoroid by examining characteristic emission lines. Elements such as sodium, magnesium, iron, calcium and other constituents can contribute to meteor spectra. This makes meteors useful remote probes of extraterrestrial material, allowing scientists to study particles that may be too small to observe directly in space.
Meteors occur as both sporadic events and meteor showers. A meteor shower happens when Earth passes through a stream of particles travelling along a similar orbit around the Sun. These streams commonly originate from comets that have released dust and debris during previous passages through the inner Solar System, although some meteor showers are associated with asteroids or active asteroid like bodies.
The meteors in a shower appear to originate from a common radiant because their trajectories are approximately parallel in space and perspective causes them to converge visually. The shower is named after the constellation or star region containing its radiant, not because the meteoroids actually originate from that constellation. The Perseids, Geminids and Leonids are prominent examples. Shower activity changes as Earth passes through different parts of the debris stream, and individual years can vary considerably in intensity.
Meteor brightness is often described using apparent magnitude, with brighter meteors having more negative magnitudes. The brightest events are classified as fireballs, although definitions can vary between observational organisations. Extremely energetic atmospheric events may produce persistent trains, sonic booms, fragmentation and widespread light. The term bolide is used inconsistently in different contexts, sometimes referring to a particularly bright fireball and sometimes to a meteor associated with an explosive atmospheric event.
Brightness alone does not reveal the exact size of the meteoroid because velocity, composition and fragmentation strongly influence luminosity. A fast fragile body can produce an impressive flash while disintegrating at high altitude, whereas a denser slower object may penetrate farther before releasing much of its energy. Estimating an object's original mass therefore requires combining multiple observations rather than simply judging visual brightness.
Meteor observations provide valuable information about atmospheric and astronomical processes. High speed meteor observations can be used to study atmospheric density, winds, temperature and composition at altitudes where direct measurements are difficult. Meteor radar systems detect ionisation trails and can measure upper atmospheric dynamics. Optical networks can reconstruct meteor trajectories and sometimes identify areas where meteorites may have fallen. Spectroscopic measurements reveal chemical signatures and can help classify meteoroid populations.
The statistical distribution of meteor velocities, radiants and brightness also provides information about the population of small bodies near Earth. Because most meteoroids are too small to detect telescopically before entry, meteor observations provide one of the main ways of studying this otherwise difficult to observe population.
The distinction between a meteor and an aurora, satellite re entry, aircraft light or other luminous sky phenomenon is based on physical behaviour and timescale. Meteors typically appear as rapid streaks lasting fractions of a second to several seconds, although persistent trains can last longer. Satellites generally move much more slowly across the sky and can remain visible for minutes. Aircraft often display blinking or repeating navigation lights and move along predictable paths.
Auroras occur over much larger spatial scales and produce diffuse, evolving structures rather than the rapid streaks typical of meteors. Some unusual atmospheric events can be difficult to classify from a single observation, which is why scientific meteor networks use multiple sensors. Modern automated cameras can identify candidate meteors and calculate their trajectories with high precision.
Meteors have also influenced human culture and scientific history. Before the development of modern astronomy, their sudden appearance was often interpreted through supernatural or religious explanations. The recognition that meteorites originate from extraterrestrial material developed gradually through careful observation and analysis of meteorite falls. The study of the L'Aigle meteorite fall in 1803 and related investigations helped establish scientific acceptance that rocks could fall from space.
Today, meteors are understood as predictable consequences of interactions between small Solar System bodies and planetary atmospheres. They are not stars falling from the sky, and they do not generally represent dangerous events. Most are produced by particles much smaller than a grain of gravel. Nevertheless, unusually large meteoroids can generate powerful atmospheric explosions, as demonstrated by the 2013 Chelyabinsk event, which produced a bright fireball and an atmospheric shock wave that damaged buildings and injured people mainly through broken glass.
