Meteors are sometimes poetically or mistakenly called shooting stars or falling stars. The streaks of light in the night sky are not stars at all, but tiny pieces of rock or dust that burn up in Earth's atmosphere. The solar system debris that causes meteors can come from primordial dust, asteroids, comets, or even soil that was dislodged from the moon or Mars. The predictable showers that occur at the same time each year are usually from comets that have shed a trail of debris as they've passed through the inner solar system on their trip around the sun.
Parts of a Meteor Shower Defined
The terms meteor, meteorite, and meteoroid are not interchangeable. Each word connotes a distinctive phase in the life of a meteor.
- Meteor - A meteor is the streak of light seen as small dust or rocky debris enters the atmosphere.
- Meteoroid - A meteoroid is the tiny rocky debris when it is in space.
- Meteorite - A meteorite is the piece of rock that was large enough to survive its journey through Earth's atmosphere and land on the surface.
There are three different types of meteorites. The majority of meteorites that reach the surface of Earth are stony in nature. Stony meteorites make up about 93 percent of all meteorites found on Earth and they can be further divided into chondrites and achondrites. Chondrites, which are made of the same dust and debris that formed Earth at the beginning of the solar system 4.5 billion years ago, are much more common than achondrites, which have been geologically processed. Besides stony meteorites, stony-iron and iron meteorites make up the last two types, with stony-iron meteorites being the rarest.
Observing Tips for Meteor Showers
Meteors can burn up in the atmosphere at any time. But some times of year produce showers (and occasionally even storms) that provide viewers with the best chances of seeing a good show. See the Annual Meteor Showers article for more information.
Astronomers use a little lingo when discussing meteor showers. A few of the terms are defined below:
- Radiant - A radiant is the portion of the sky that the meteors appear to emanate from. Because meteor showers occur when Earth enters a stream of debris, meteors associated with this shower can all be traced back to the same portion of sky. For example, the Orionid meteor shower produces meteors that seem to come from the constellation Orion.
- Zenithal Hourly Rate - Also known as ZHR, the zenithal hourly rate describes how many meteors an observer can expect in an hour under dark skies and with the radiant nearly overhead (at zenith). Showers can range from a ZHR of 6 to 100. An amazing ZHR of 150,000 was estimated for the 1966 Leonid meteor shower (storm) at its peak.
- Bolide - A bolide is another term for a fireball, or a large size rock that burns up in the atmosphere, producing a more spectacular show. The source of some bolides are large enough to reach the ground as meteorites, and occasionally do damage on Earth.
A fun fact about meteors is that you can hear a meteor shower on your radio. In fact, more meteors can be heard than seen. In order to hear them, set your FM radio to a distant known station frequency that you can't hear. The meteor and its ionized trail will reflect the radio signal, allowing you to catch occasional snippets of that station.
 |
