What Happens During a Meteor Shower?

Meteor Showers

• As the earth orbits the sun, it periodically encounters planetary debris, such as dust and tiny rock particles. This debris, usually smaller than a grain of sand, enters the atmosphere at high rates of speed, creating heat from friction. The heat causes them to vaporize, leaving a visible streak in the sky. When the planet passes through a dense field of this debris, a large number of meteors occur, called a meteor shower. These showers commonly occur at regular intervals and appear to come from a particular area of the sky.

Meteor Shower Radiant

• While the meteors actually travel on parallel trajectories, perspective causes them to appear to originate from a single point. This is the same effect that makes railroad tracks appear to converge in the distance. The apparent point of origin is called the shower's radiant. Meteor showers are commonly named for the constellation in which their radiant occurs. For example, the Leonid meteor shower has a radiant in the constellation Leo.

Source of Meteor Showers

• Space contains lots of debris left over from the creation of the solar system, but this debris is very sparse. This type of debris only produces sporadic meteors, typically at a rate of between two to 16 per hour. Meteor showers require much more debris. This debris comes from the deterioration of comets. As comets approach the sun and vaporize, they leave behind a meteoroid stream of dust and tiny rock particles. It is these streams, when the earth passes through them, that produce meteor showers.

Factors Affecting Meteor Showers

• The rate and brightness of meteor showers is affected by several factors. The age of the stream impacts the amount of debris available. The stream's density and distribution determine the rate at which the debris enters the atmosphere. Shower intensity is also impacted by how closely the earth passes to the stream's core. Finally, the composition of the debris affects how bright the meteors will appear to viewers.

Meteor Outbursts and Storms

• When a given meteoroid stream produces a very high rate of meteors, the event is called a meteor outburst or storm. This typically occurs when rates exceed 1,000 meteors per hour, or one per second. Outbursts and storms typically occur during the month of November.

Meteor Shower Example

• The Perseid meteor shower occurs in August. It is a result of the meteoroid stream produced by the Swift-Tuttle comet, which orbits the sun every 133 years. As the earth passes through its debris field, particles strike the atmosphere at 140,000 miles per hour, creating a visible shower of meteors. While a typical meteor shower lasts a few days, the debris field from this comet is so wide that it takes the earth several weeks to completely pass through it.