Meteors and Their Sources

A meteor is any small object--from tiny grains of dust to rocks the size of baseballs, and larger--that enters the Earth’s atmosphere. Meteors travel at very high speeds, ranging from 10-45 miles per second. When a meteor runs into the Earth’s atmosphere, it heats up to several thousand degrees Fahrenheit, and begins to glow. Once meteors get hot enough, they vaporize, leaving the trail we know as a “shooting star.” The vast majority of meteors vaporize entirely in the atmosphere, and never strike the Earth.

Many meteors are solitary chunks of debris that happen to cross Earth’s orbital path. They may be left over from planetary formation early in the solar system’s history, or they may have broken off during collisions between asteroids or other bodies. Meteor showers, however, are associated with comets. Comets leave a trail of debris behind them as they travel near the Sun. If a comet’s orbital track happens to cross that of the Earth, the dust-like particles it leaves behind will be swept up by our planet every time we cross that point in our own orbit. And because we will cross the same point in our orbit once every year, meteor showers occur at the same times every year.

Major meteor showers visible from the Northern Hemisphere, and the dates they usually occur:

Quadrantids: End of December-beginning of January
Lyrids: Mid-April
Eta Aquarids: late April through May
Perseids: Mid-July through Mid-August
Orionids: Through most of October
Taurids: October
Leonids: Mid-November
Geminids: Early to mid-December

The Eta Aquarids and Orionids both come from the famous Halley’s Comet, which crosses Earth’s orbital path in two places.

Meteor storms vary in intensity; often they are at their best when their parent comet has recently passed near the Sun, replenishing the dust streams behind them. Astronomers can usually predict the nights when a meteor shower will peak.

Of course, weather is a factor in observing meteor showers. Clouds or fog will obscure them. Bright moonlight will make meteors harder to see, as will proximity to artificial light, such as that from cities or towns.

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