As this dust drifts around and is swept up by the gravitational field of the earth, it will enter the atmosphere from random directions. About 400 tons of it falls to Earth each day, mostly unoticed. Occasionaly a piece will be massive enough and enter at high enough velovity that friction with the atmosphere will heat it up and it will glow bright enough and release enough energy to ionize the air surrounding it and in dark skies, a meteor is seen. The rate of these random meteors is about 5 to 10 an hour and should be observable on any dark clear night. This background of random meteors is called sporadic meteor activity.
Sporadic meteors differ from meteors of the annual showers only in their random nature.
The annual showers arise from concentrations in dust and debris that are in an orbital path, or stream, that crosses the Earth's orbit. Meteors from a stream will enter the Earth's atmosphere from the same general area. The observed effect from the surface is that imaginary lines, traced backwards along the tragectory of each meteor, will intersect within an 8 degree circle. Meteors tragectories that do not intersect within that area are usualy sporadics but may be from another shower. There are times when several showers are active simultaniously, six are active when the Perseids peak on August 12th.