Rainbow and Rays Over the Czech Republic

May 13, 2010


Photographer: Edwin Proctor
Summary Author: Edwin Proctor; Jim Foster

The photo above showing a magnificent double rainbow was taken just south of the city of Kromlov in the Czech Republic in June of 2009. A lot can be learned about a scene just by observing such a bow. For a rainbow to attain such grandeur, the Sun must be close to the horizon; near sunset or sunrise (sunset in this case). There’s always a secondary or outer bow -- physics or raindrop refraction and reflection requires it. However, in many cases, the secondary bow is simply too dim to easily detect. It can never be as bright as the primary bow; though, since some light is lost with each reflection. At best, it’s approximately 43% of the brightness of the primary bow. Notice the faint rays slicing across the bows. These are anticrepuscular rays. They actually give an indication of the sky condition on the opposite horizon; the horizon where the Sun is setting. If rays are visible on the eastern horizon, cloud turrets as well as crepuscular rays are likely visible on the western horizon. Of course, it’s the presence of clouds and their positioning that block out some of the sunlight (dark rays) and permit some light to break through (bright rays).