Meteors, Meteoroids and Meteorites: What's the Difference?

You are lying on a blanket under a dark sky when a streak of light flashes overhead and vanishes.

Most people call it a shooting star.

An astronomer might call it a meteor, and the tiny object that caused it a meteoroid.

If a piece of it had reached the ground, that would be a meteorite.

These three words are easy to mix up,

but the difference is simple once you see that they describe the same object at different stages of its journey.

Here is what each term means, what makes a meteor glow, where meteor showers come from and how to enjoy them.

Three Words, One Journey

The easiest way to keep the terms straight is to remember where the object is:

A handy memory trick: a meteorite is the one that made it all the way down to the ground.

Meteoroids: Small Travelers in Space

A meteoroid is a small chunk of rock or metal orbiting the Sun.

Astronomers generally use the term for objects ranging from tiny grains up to about a meter across.

Anything bigger is usually called an asteroid, and anything smaller than a speck of fine dust is simply interplanetary dust.

Most meteoroids are fragments knocked off asteroids in collisions or bits of dust shed by comets.

A small number come from the Moon or Mars, blasted into space by large impacts.

Earth sweeps up an enormous amount of this material; estimates vary widely,

but tens of tons of dust and small debris fall on our planet every day,

almost all of it too small to notice.

Meteors: The Flash in the Sky

When a meteoroid meets Earth's atmosphere, it is moving extremely fast, somewhere between about 11 and 72 km per second (roughly 25,000 to 160,000 mph).

At that speed, it rams into the air so violently that it compresses and heats the air in front of it.

The meteoroid's surface vaporizes, and the hot, glowing gas creates the streak of light we see.

Most meteors light up roughly 80 to 120 km (50 to 75 miles) above the ground, far higher than airplanes fly.

Surprisingly, the majority are caused by particles no bigger than a grain of sand or a small pebble.

They are bright not because they are large, but because they are so fast.

Fireballs and Bolides

A fireball is an exceptionally bright meteor, generally defined as one brighter than the planet Venus.

Fireballs are produced by larger meteoroids and can sometimes light up the landscape or show colors.

A fireball that explodes in a bright flash is often called a bolide.

In 2013, a meteoroid roughly 20 meters (65 feet) across exploded over Chelyabinsk, Russia;

its shock wave shattered windows across the city, and around 1,500 people were hurt, mostly by broken glass.

Meteorites: The Survivors

Most meteoroids burn up completely.

Only relatively large or sturdy ones survive the fiery descent and reach the ground as meteorites.

Freshly fallen meteorites usually have a thin, dark, glassy coating called a fusion crust, formed as the outer layer melted during the fall.

Meteorites are named after the place where they fell or were found, and they fall into three broad groups:

• Stony meteorites are by far the most common among observed falls. Many contain tiny round grains called chondrules, some of the oldest solid material in the solar system, about 4.6 billion years old.
• Iron meteorites are made mostly of iron and nickel metal. They are much rarer among falls but easy to recognize, and many are thought to come from the cores of shattered early asteroids.
• Stony-iron meteorites are a rare mix of metal and rock, and some contain beautiful gem-like crystals.

The largest known meteorite, the Hoba meteorite in Namibia, is a slab of iron weighing about 60 tonnes that still rests where it was found.

Much larger impacts leave craters instead; Meteor Crater in Arizona, more than a kilometer across,

was blasted out by an iron meteoroid tens of thousands of years ago.

Meteor Showers Explained

On any dark night you might see a few random meteors per hour.

During a meteor shower, the rate can rise to dozens per hour under ideal conditions.

Showers happen when Earth passes through a trail of debris left behind by a comet, or occasionally an asteroid, along its orbit.

Because all the particles in a trail travel in parallel,

their meteors appear to fan out from a single point in the sky called the radiant.

Each shower is named after the constellation where its radiant lies. Some of the best-known annual showers are:

• The Quadrantids, with a short, sharp peak in early January.
• The Perseids, peaking in mid-August, from debris of Comet Swift-Tuttle.
• The Orionids, in October, made of dust from Halley's Comet.
• The Geminids, peaking in mid-December, one of the richest showers of the year, unusual because its source is an asteroid-like object rather than an obvious comet.

How to Watch Meteors

1. Find a dark site away from city lights, with a wide view of the sky.
2. Check the Moon. Bright moonlight washes out fainter meteors, so nights with little or no Moon are best.
3. Get comfortable. Lie back on a reclining chair or blanket and dress warmly, even in summer.
4. Skip the telescope. Meteors move too fast and across too much sky; your eyes are the ideal instrument.
5. Let your eyes adapt. Allow 20 to 30 minutes in the dark and avoid looking at your phone's bright screen.
6. Stay up late. Rates are usually higher after midnight, when your side of Earth faces forward in its orbit and runs into more particles.

Frequently Asked Questions

Are meteorites hot when they land?

Usually not.

The intense heating lasts only a few seconds and affects only the outer layer, which melts and is stripped away.

By the time a small meteorite reaches the ground, it has typically slowed down and cooled,

and many are only warm or even cold to the touch.

Is it dangerous to be hit by a meteorite?

The risk to any individual is extremely small. Most meteorites fall into oceans or empty land.

There are only a few well-documented cases of people being struck,

such as a woman in Alabama who was bruised by a meteorite that crashed through her roof in 1954.

How can you tell if a rock is a meteorite?

Many meteorites are heavy for their size, have a dark fusion crust and attract a magnet because they contain iron-nickel metal.

Most suspected meteorites, however, turn out to be ordinary Earth rocks or industrial slag.

If you think you have found one, contact a natural history museum or university geology department,

and keep in mind that rules about collecting rocks vary by country and landowner.

Catch a Falling Star

Every meteor you see is a tiny piece of the solar system's history meeting its end in a flash of light.

Now that you know the difference between meteoroids, meteors and meteorites, pick a dark night during the next major shower,

lie back and watch the sky. Patience is almost always rewarded.