Small rocky and/or icy particles that are swept up by the earth in its orbit about the sun. Also called "shooting stars", they travel across the sky in a very short time, from less than a second to several seconds, and they do so because they are only a matter of tens of miles above the surface of the earth. Meteor showers are generally thought to be produced by the debris left by comets as the latter orbit the sun. (Comets, on the other hand, are not in our atmosphere but are much further away than is our own Moon; therefore, comets do not "streak" across the sky as do meteors -- a common misconception among the general public. )