On August 13, after a rainshower had passed over Bochum, Germany, a twinned rainbow appeared. The bow was rather faint, but the twinning in its upper part was clearly visible. The red and the yellow colour bands of the rainbow were twinned.
On photographs of the rainbow, the twinning effect is hardly visible, but after oversaturating one of the pictures, the twinning turned out well.
During the rainshower, large drops were falling. A second shower about half an hour later with normal-sized drops also produced a rainbow. Even though this bow was very bright, it was not twinned, but showed a secondary bow and supernumeraries.
This is another hint for the theory to be right that the effect of twinned rainbows is really produced by large raindrops getting flattened by the resistance of the air when falling.
Author: Peter Krämer, Bochum, Germany