Rainbow

A rainbow is most often viewed as a circular arc in the sky. An observer on the ground observes a half-circle of color with red being the color perceived on the outside or top of the bow. Those who are fortunate enough to have seen a rainbow from an airplane in the sky may know that a rainbow can actually be a complete circle. Observers on the ground only view the top half of the circle since the bottom half of the circular arc is prevented by the presence of the ground. Yet observers in airborne planes can often look both upward and downward to view the complete circular bow. The circle results because there are a collection of suspended droplets in the atmosphere that are capable of concentrating the dispersed light at angles of deviation of 40-42 degrees relative to the original path of light from the sun. These droplets actually form a circular arc, with each droplet within the arc dispersing light and reflecting it back towards the observer.