Meteors are luminous atmospheric phenomena produced when extraterrestrial solid material enters a planetary atmosphere at high velocity and interacts strongly with atmospheric gases. On Earth, the visible light commonly associated with a meteor arises from a combination of processes including heating, excitation and ionisation of atmospheric molecules and atoms, together with ablation and fragmentation of the incoming body. The object responsible is generally called a meteoroid while it is in space.
The term meteor therefore refers primarily to the phenomenon observed in the atmosphere rather than to the solid object itself. Very bright meteors are often called fireballs, while exceptionally energetic events can be described using more specialised terminology. Meteors can occur sporadically when individual particles enter Earth's atmosphere or in organised meteor showers when Earth passes through a stream of debris associated with a parent body.
Atmospheric entry begins when a meteoroid encounters increasingly dense gas as it approaches Earth. The object experiences aerodynamic drag, which reduces its velocity and converts kinetic energy into thermal and other forms. Compression and heating of the surrounding gas produce high temperatures and intense excitation. Material can ablate from the surface and enter the surrounding flow as vapour and fragments. The visible luminous trail is not simply a glowing rock heated uniformly from the outside. Atmospheric plasma and excited species contribute substantially to the emitted light, while the physical object can undergo fragmentation, melting and vaporisation. The brightness depends on mass, velocity, composition, shape, atmospheric density, entry angle and fragmentation behaviour.
Meteors can travel at very high velocities relative to Earth because their heliocentric orbits combine with Earth's orbital motion. The possible geocentric entry speed has a lower bound set by Earth's gravitational attraction and the relative orbital geometry, while very fast retrograde encounters can produce much higher speeds. As the object penetrates the atmosphere, drag generally increases as atmospheric density rises, causing rapid deceleration.
Ablation is strongest where atmospheric conditions and velocity produce intense heating, although the exact energy transfer depends on shape and flow regime. The meteor may cease glowing when the remaining material slows sufficiently or fragments completely. The visible path can therefore end at high altitude even though some fragments may continue downward as dark flight and potentially reach the ground as meteorites.
Meteor showers occur when Earth intersects streams of debris distributed along the orbit of a comet or, in some cases, an asteroid. The particles enter Earth's atmosphere from similar directions and with related heliocentric orbital characteristics. The apparent point in the sky from which the meteors seem to originate is called the radiant, although the particles themselves travel along nearly parallel trajectories and the perspective effect makes their paths appear to diverge from a point.
Meteor showers are often named after the constellation or star region containing the radiant. The intensity of a shower varies with the density and distribution of the debris stream, Earth's position within it, lunar illumination, observing conditions and the observer's location. Individual shower meteors can differ considerably in brightness and duration.
The colour of a Meteor can provide information about the physical and chemical processes occurring during entry, although visual colour interpretation is complicated. Different excited atmospheric species emit at characteristic wavelengths, while elements ablated from the meteoroid can contribute their own spectral lines. Spectroscopy can therefore reveal information about the composition of the incoming material. Sodium, magnesium, iron and other elements can produce identifiable emissions in meteor spectra, while atmospheric nitrogen and oxygen also contribute. The observed spectrum depends on temperature, density, velocity and chemical composition. Professional meteor spectroscopy can consequently provide information that cannot be obtained from simple visual observation. Brightness measurements and multi station observations can also allow researchers to reconstruct trajectories and estimate physical properties.
Meteors are distinct from meteorites. A meteor is the transient luminous phenomenon in an atmosphere, whereas a meteorite is solid extraterrestrial material that survives passage through the atmosphere and reaches the ground. Many meteors are produced by particles too small to survive, so no meteorite results. Conversely, a meteorite can sometimes be associated with a very bright fireball that was recorded by multiple observing stations.
The path of a meteor can be reconstructed from simultaneous observations from different locations, allowing the atmospheric trajectory to be determined geometrically. If the trajectory and deceleration are sufficiently well constrained, researchers can estimate where surviving fragments may have landed and search for a meteorite fall.
Meteor observations have scientific applications beyond public astronomy. Networks of cameras and radar instruments monitor meteor activity to determine trajectories, orbital properties and population statistics. Meteor radar can detect very small particles that are invisible to ordinary optical systems and can measure atmospheric winds at relevant altitudes through the motion of ionised trails. Optical networks can triangulate bright meteors and identify possible meteorite fall locations. Meteor observations also provide information about the distribution and evolution of meteoroid streams. Because meteor activity is connected to parent bodies and orbital dynamics, long term observations can help track changes in debris populations.
Meteors illustrate the interaction between extraterrestrial matter and planetary atmospheres. Their behaviour depends on both the properties of the incoming body and the physical structure of the atmosphere. Earth provides an especially favourable environment for observation because its atmosphere is sufficiently dense to produce abundant luminous events while still allowing some larger bodies to survive. Other planets and moons with atmospheres can also produce analogous phenomena, although entry conditions differ substantially.
Meteors are therefore not objects in the same sense as Asteroids or Meteorites but observable physical events caused by atmospheric entry. Their study connects celestial mechanics, atmospheric physics, plasma processes, spectroscopy, impact science and planetary materials, making them useful indicators of the material continually arriving from interplanetary space.
