Most are white or blue-white in appearance, although other frequent colors are yellow, orange. The colors seem more related to the speed of the meteor rather than composition. Red meteors occasionally appear as very long streaks and are usually indicative of a meteor that is skimming the atmosphere. Green meteors are also occasionally seen and are usually very bright. The green color may be a result of ionized oxygen.
Meteoroids are the smallest particles orbiting the sun, and most are no larger than grains of sand.
From years of studying the evolution of meteor streams, astronomers have concluded that clouds of meteoroids orbiting the sun were produced by comets. Meteoroids can not be observed moving through space because of their small size. Over the years numerous man-made satellites recovered by manned spacecraft have shown pits in their metal skins which were caused by the impact of meteoroids. Meteoroids become visible to observers on Earth when they enter Earth's atmosphere. They are then referred to as meteors.