Meteors

Core Concepts

The naming ladder: meteoroid → meteor → meteorite

The same object gets different names at different stages: in space it is a meteoroid (a solid body smaller than an asteroid); entering the atmosphere and producing light, it is a meteor (a "shooting star"); if part survives to the ground, it is a meteorite. A meteor is an event, not an object — this three-part vocabulary is the single most tested distinction in the topic.

What actually creates the light

A meteoroid does not catch fire. Plowing through air at tens of kilometers per second, it compresses the atmosphere ahead of it, heating the air to thousands of degrees; the surface layer melts and vaporizes (ablation), and the glowing trail is a mix of hot vaporized rock and ionized air. That ion trail reflects radio waves, which is how radar detects meteors in daylight. Most meteoroids are fully vaporized between roughly 80 and 120 kilometers up — high enough that fallen meteorites are cold when they land, not hot.

Meteor showers and radiants

A meteor shower occurs when Earth passes through a stream of debris left along a comet's (or rarely an asteroid's) orbit. The particles travel on nearly parallel paths, so they appear to radiate from one point on the sky, the radiant — the same perspective effect that makes parallel railroad tracks seem to meet. Showers are named for the constellation containing the radiant: the Perseids (mid-August, parent comet Swift-Tuttle), the Leonids (mid-November, comet Tempel-Tuttle, famous for occasional storms of thousands per hour), and the Geminids (mid-December, parent 3200 Phaethon, often the year's best). A shower's quoted hourly rate is the commonly taught "zenithal hourly rate" (ZHR): how many meteors one observer would count under ideal conditions.

Fireballs and bolides

A fireball is a meteor brighter than Venus (roughly magnitude −4), bright enough in rare cases to cast shadows. A bolide is a fireball that breaks up or explodes in the atmosphere, sometimes with a sonic boom. The 2013 Chelyabinsk event — an estimated ~20-meter asteroid that exploded at altitude, injuring about 1,500 people, mostly from flying glass — is the best-documented recent example, showing that airbursts, not just ground impacts, are a real hazard. Tracked fireballs can also yield freshly fallen meteorites when fragments are recovered.

Where meteoroids come from

Meteoroids have two main sources. Comet debris is fluffy, icy, and fragile; it produces most shower meteors, and the particles are so delicate they almost never survive to the ground. Asteroid collisions produce denser, stony or metallic fragments that give sporadic (non-shower) meteors and are the usual parents of meteorites. The Geminids are the notable exception — a stream from an asteroid-like body, showing the comet–asteroid boundary is not always clean.

How It Works / Step-by-Step Process

1. A meteoroid on an Earth-crossing orbit enters the upper atmosphere at 11–72 km/s.
2. Air ahead is compressed and heated to thousands of degrees; the surface melts and vaporizes (ablation), ionizing a trail of air.
3. The glowing trail — the meteor — lasts under a second, typically starting 80–120 km up, as the meteoroid loses mass and speed.
4. If a large, dense fragment survives to the ground (slowing to free-fall speed), it lands as a meteorite — cold, with a dark fusion crust.
5. During a shower, many stream particles do this at once, all appearing to come from the radiant.

Common Confusions