Inside the Primary Rainbow
June 12, 2004
This rainbow arched over southern Ohio on March 30, 2004. The sky on the inside of rainbows is always brighter than on the outside because more sunlight has been scattered in that direction by raindrop reflections. Although rainbows result from the concentration of rays of sunlight that emerge from raindrops at an extreme angle, light also emerges from droplets at smaller angles. It rurns out that those light rays undergoing single reflections in raindrops not only form the primary rainbow but brighten the sky inside it. Alexander of Aphrodisias first described the effect in 200 AD, and the dark band between the primary and secondary bows now carries his name. Notice the faint secondary rainbow (brightest on left) perched above the primary bow.
Photo details: Nikon D-100 with fisheye lens.