A comet's tail is composed of material from the comet body (usually a frozen ball of ice and minerals) in particle form, stripped and pushed away from the comet by solar winds and radiation. Comets do not present a tail until they reach a certain distance from the Sun; at this point, the comet's own inertia pushes against the solar winds, vaporizing material from the comet, which streams out behind the comet in a tail. The tail is visible when Sunlight reflects off the particles. As the comet moves closer to the Sun, more and more material is stripped from it, and solar winds act on it to a greater degree. This causes the tail to appear brighter. The tail will always point away from the Sun, since the solar winds come directly from the Sun in a straight line; even when the comet seems to be moving parallel to the Sun, the tail will point away. Variations on the tail occur due to material composition, speed, and magnetic fields. The tail is an extension of the comet's coma, a large field of gas and dust surrounding the comet.