"Blue Hour" is the period of twilight early in dawn each morning and late dusk each evening when the sun is at a significant
distance below the horizon and the residual, indirect sunlight takes on a predominantly blue hue. During the blue "hour"
(typically the period is about 40 minutes in length), red light passes straight into space while blue light is scattered in the
atmosphere and therefore reaches the earth's surface. Because of the quality of the light, this period is prized by artists.