Find a Double Rainbow Day
“Saturday is full of orange oranges,
Sunday is full of pink apples,
Monday is full of green limes,
Tuesday is full of red watermelons,
Wednesday is full of blue blueberries,
Thursday is full of purple grapes,
Friday is full of yellow bananas, and,
The week is full of rainbow fruit.”
~ Anthony T. Hincks
If you're lucky enough to see a rainbow against a dark sky, look for the double rainbow. A double rainbow occurs when the light is reflected twice in the drop, yielding two different reflections from different angles. The secondary rainbow (which is higher and lighter in color than the primary) has the colors reversed. The double rainbow is always present somewhere but is not always visible to the observer for reasons of geometry and background light intensity. The darker band seen between the double rainbows, is an optical phenomenon first described by Alexander of Aphrodisias in 200 A.D..
The term double rainbow is used when both a primary and secondary rainbow are visible. In theory, all rainbows are double rainbows, but since the secondary bow is always fainter than the primary, it may be too weak to spot in practice. In a double rainbow, a second arc is seen outside the primary arc, and has the order of its colours reversed, with red on the inner side of the arc. This is caused by the light being reflected twice on the inside of the droplet before leaving it.
This tartan by designer Steven Patrick Sim, employs the vivid hues of a double rainbow against a dark sky.
From the register notes:
This tartan was inspired by an unusually bright double rainbow which appeared over Arbroath on 9th May 2014. Designed to celebrate Scotland's skies the tartan pays tribute to the Scottish rains and sunlit rainbows. The sett reflects the seven colours of the spectrum and portrays Alexander's Dark Band, the optical phenomenon associated with rainbows and named after Alexander of Aphrodisias who first described it in 200 AD. The grey pivot represents the second bow. The blue, purple and grey pay tribute to the sky and to Scotland's streams, rivers and lochs. The tartan is intended for any individual or group wishing to be represented by a rainbow-themed tartan. Visit the registrant's website for the full rationale behind the design.
For more fascinating double rainbow facts, click the double rainbow captured in the Tweed Valley in the Scottish Borders by photographer Graham Riddell.