Almost everyone has seen a `shooting star' or `falling-star'.

What we are witnessing is a small piece of interplanetary matter, called a meteor, entering the Earth's atmosphere and `burning up' at a height of about 50 to 75 miles above us.

These small bits of matter (most are about the size of a grain of sand, according to scientists) are moving very fast relative to the Earth with speeds from 7 to 46 miles (11 to74 kilometers) per second. When they enter the Earth's atmosphere they are rapidly slowed down. This means that they lose a lot of energy which appears as heat and light. Both the particle and the air that is forcing its way past are made very hot. The particle, unless it is large, is completely vaporized and the air in the path of the meteor is ionized. We see light from the emission of radiation from the ionized gas and from the white hot evaporating particle. The trail is the hot gas gradually cooling down. It may last for less than a second or in the case of large meteors, several minutes. Large bright meteors are often called "fireballs."A very large fireball can be seen over a distance of 200 miles or more.

While most meteors look white, some appear blue, green, yellow, orange, or red. One that explodes at the end of its visible flight is called a bolide. At certain times of the year we see more meteors than usual. This happens when Earth passes near a comet's orbit and sweeps through debris that the comet has shed. Such events are called meteor showers. For the major annual meteor showers, seeing one meteor every few minutes is typical, though there are often bursts and lulls.

Shower meteors can appear anywhere in the sky, but their direction of motion is away from the constellation whose name the shower bears. This apparent point of origin is known as the radiant. The most well known annual meteor shower is the Perceids which appears in the 2nd week of August. Because of the good weather in the Northern Hemisphere, people are often outside to witness this shower. But the most spectacular meteor shower is the Leonids which has produced the phenomena of the meteor "storm" - meteors falling at the rate of thousands per hour, sometimes thousands per minute.

Occasionally a larger object will survive its descent and fall to Earth -- then it's called a meteorite.