© Michael Theusner/Applied Optics.The third-order (tertiary) rainbow (left), accompanied by the fourth-order (quaternary) rainbow (right). They appear on the sunward side of the sky, at approximately 40° and 45°, respectively, from the Sun. This is the first picture ever of a quaternary rainbow in nature and the second picture ever of a tertiary rainbow.
Forget the double rainbow. This year, the quadruple rainbow is all the rage.
A new photograph shows the first-ever evidence of an elusive fourth-order rainbow.
Few people have ever claimed to see even three rainbows in the sky at once. Scientific reports of these phenomena, called tertiary rainbows, were so rare - only five were reported in 250 years - that until now many scientists believed they were as real as a pot of gold at the end of a rainbow.
These legendary optical rarities, caused by three reflections of each light ray within a raindrop, have finally been confirmed, thanks to photographic perseverance and a new meteorological model that provides the scientific underpinnings to find them. The work is described in a series of papers in a special issue published this week in the journal Applied Optics.
The optical treasure hunt even went one step further, as revealed in the photo that shows the shimmering trace of a fourth rainbow.
