Meteoroid, meteor, meteorite
Three similar words describe the same object at different stages:
| Term | What it means |
|---|---|
| Meteoroid | A small rocky or metallic body traveling through space, smaller than an asteroid |
| Meteor | The flash of light produced when a meteoroid enters the atmosphere |
| Meteorite | Any part of the object that survives the fall and reaches the ground |
So the meteor is not the object itself but the visible event. Most meteoroids are tiny and burn up completely, so only a small fraction of meteors ever produce meteorites.
How a meteor forms
Meteoroids hit Earth’s atmosphere at speeds between about 11 and 72 km per second. At those speeds, the air in front of the particle is compressed and heated violently. The particle’s surface vaporizes, and the hot gas and air along its path glow. The result is a thin line of light that lasts a fraction of a second to a few seconds.
Faster meteoroids produce brighter meteors for their size, because the energy they carry rises sharply with speed. That is why a grain the size of a sand particle can create a streak visible from the ground.
Some meteors leave a persistent train, a faintly glowing trail that remains for a few seconds or, rarely, minutes after the meteor fades.
Fireballs and bolides
A meteor that is brighter than the planet Venus is often called a fireball. Very bright fireballs, especially those that explode or break apart in the atmosphere, are called bolides. Fireballs can be caused by objects a few centimeters to meters across. These larger objects are the ones most likely to drop meteorites.
Sporadic meteors and meteor showers
On any clear, dark night you can see a few random meteors each hour. These are called sporadic meteors. They come from scattered debris that is not part of any particular stream.
A meteor shower happens when Earth passes through a stream of debris left by a comet or, sometimes, an asteroid. All the particles in the stream travel in parallel paths, so from the ground their meteors appear to spread out from a single point in the sky, called the radiant. The shower is named after the constellation where the radiant lies, such as the Perseids from Perseus or the Geminids from Gemini.
Because Earth crosses each stream at about the same point in its orbit each year, showers return on roughly the same dates. See the meteor shower calendar for the main showers and their peaks.
Where meteoroids come from
Most shower meteoroids are dust and grains released by comets as they approach the Sun and their ice evaporates. Over time, this debris spreads along the comet’s orbit. Other meteoroids are fragments of asteroids broken off in collisions. A very small number of meteorites have been identified as coming from the Moon or Mars, blasted off by large impacts.
How to see more meteors
- Go somewhere dark. Light pollution hides the many faint meteors.
- Avoid moonlight. A bright Moon cuts the number you see. The moon phases show when nights are darkest.
- Watch after midnight. In the early morning hours, your side of Earth faces the direction the planet is moving, so it sweeps up more meteoroids.
- Use your eyes only. A wide view of the sky matters more than magnification.
- Be patient. Allow time for your eyes to adapt, and watch for at least half an hour.