A Brocken spectre, a kind of shadow that is greatly magnified and fringed by rainbow colors, is cast by a person standing on a mountain onto a cloud at a lower altitude. It is named after the mountain 1) on which it was first spotted. In actuality, it is an optical illusion. The mist of the cloud alters the viewer’s depth perception, making the shadow appear larger and more 2) distantly than expected. A Brocken spectre can be seen only under specific conditions. The sun must be directly behind the person, and there must be 3) many water droplets suspended in the air. Sunlight penetrates these droplets and reflects off the opposite side, emerging to come back toward the sun. This sunlight 4) coming back toward the sun interferes with itself, making circular zones of darkness and brightness, and creating a phenomenon called diffraction. This is 5) what causes the rainbow colors to appear on the shadow’s edges.