What is a meteor shower ?
A meteor shower is one of nature's most breathtaking scenes, but as wonderful as they are to gaze upon, they are even more amazing when you know what causes them!
To understand a meteor shower though, we must first cover a few terms:
METEOROID:
A meteoroid is a particle of dust or rock floating in the Solar system. Meteoroids typically come in sizes as small as sand to as large as a boulder.
METEOR (SHOOTING STAR):
When a meteoroid enters the Earth's atmosphere, air friction causes the meteoroid to vaporize in a streak of fire. This is known as a meteor but is commonly called a shooting or falling star.
METEORITES:
When a meteoroid is large enough, it doesn't vaporize completely and some fragments reach the Earth's surface. These fragments are then called meteorites. Most meteoroids are vaporized in the atmosphere and never make it to the surface, so these are pretty rare.
METEOR SHOWER:
A meteor shower (sometimes called a meteor storm) occurs when a large number of meteors appear to fall, or "radiate", from a single point of origin in the sky.
Origin
So, that answers the basic question of what a meteor shower is, but what causes them? Where do meteoroids come from?
The answer is comets.
A comet is a big ball of dirt, rock and ice that orbits the sun. Typically, a comet's orbit takes it to the outer most reaches of the solar system. The comet starts to heat up as it approaches the sun, and bits of rock break away. These bits of rock maintain the same direction and speed as the comet, and thus create a stream of debris. This is what appears as the comet's tail. The solid pieces of debris have just become meteoroids.
The meteoroids maintain the same orbital path as the comet from which they broke apart. As Earth orbits the sun, it can pass through the stream of meteoroids and a meteor shower is born.
The meteoroids fall into the atmosphere at a very high speed and begin to streak through the air. The particles are vaporized by the friction caused by going from the vacuum of space into the Earth's atmosphere. As the particles vaporize, a streak of light is created that quickly disappears. When there a many meteoroids, this is called a "meteor storm."
Since most meteoroids are the size of a grain of sand, very few survive the entry into Earth's atmosphere to make it to the surface and become meteorites.
Because the meteoroids came from the same comet and all share the same path, they appear to the observer on Earth to radiate from a single point in the sky. This is an effect of the observer's perspective. Imagine lying on a set of railroad tracks and looking off toward the horizon. The tracks appear to converge at a single vanishing point on the horizon. It's the same effect with meteor showers.
Meteor showers are usually named for the constellation from which they appear to radiate. One of the most visible meteor showers is the Perseids. The Perseids radiate from the constellation Perseus and peak around August 12th of each year with rates of over one meteor per minute.
One of the most spectacular meteor showers is Leonids. As the name implies, this shower radiates from the constellation Leo and can be seen from November 17th to November 19th. Approximately every 33 years, the comet that spawns the Leonids returns to the solar system and the resulting Leonid shower can reach as many as hundreds of thousands of meteors per hour.
The good news is that you don't have to wait for a meteor shower to catch a falling star. Since meteoroids enter our atmosphere on a regular basis, any given night you can typically see a few meteors in an hour.
The best conditions are typically cold nights, when the moon is new. And be sure to get away from the light pollution of any nearby cities or towns.
Happy star gazing!
M. Beck
