METEOROID STREAMS AND THE SPORADIC BACKGROUND

There is a general agreement that meteoroid streams form through the e jection of dust grains, or meteoroids, up to a few centimeters in size from comets and possibly asteroids. After ejection these meteoroids a re subject to forces arising from Solar radiation and the gravitationa l fields of the planets. Meteoroids may also break up into smaller one s through collisions and other effects. In many cases meteor showers h ave been observed for millennia, with material being fed into the stre am throughout this period from the parent and material lost through th e external effects mentioned. Much of the lost material forms the gene ral sporadic background. This paper will review our state of knowledge of the processes involved above and will also aim to give some insigh t into the structure of the sporadic background.