A United Kingdom police helicopter spotted a full-circle rainbow during a recent flight, and it is a spectacular and rare view of a beloved natural phenomenon.
As the New York Post writes, the National Police Air Service (NPAS) in the South West and Wales Region police chopper saw the circular rainbow over the Vale of Glamorgan, a county borough located just to the west of Cardiff, the largest city in Wales.
— NPAS South West & Wales Region (@NPASSouthWest) November 6, 2023
Although rainbows are most commonly spotted by people on the ground, unsurprisingly, the trademark arc shape is not the entire rainbow. The unusual-looking circle photographed in Wales is what all rainbows would look like if people were at the optimal viewing position. From the Earth’s surface, people can “only see light reflected by raindrops above the horizon,” explains National Geographic.
It is also true that the appearance of a rainbow depends on a person’s antisolar point, the hypothetical point precisely opposite the Sun that is the center of a primary rainbow. No two people can occupy the same antisolar point and, thus, will never see a rainbow in an identical way.
The refractive index of the water droplets in the atmosphere determines the radius of a rainbow. The more that a ray of light refracts, or bends, as it passes from air to water, the higher the refractive index and the smaller the rainbow. Saltwater has a higher refractive index than fresh water, so rainbows created by sea spray are smaller than those formed by rain. The rainbow seen in Welsh skies was caused by freshwater in the atmosphere.
Last year, PetaPixel featured an image taken by a photographer with a drone that shows a circular rainbow. Coincidentally, the photographer, Nick Sidle, was also in the United Kingdom, albeit in the Scottish Highlands, much further north than southwestern Wales.
Sidle used his DJI Mavic 3 to get very close to the rainbow. His drone was so near the colorful display that he had to stitch together multiple images to show the entire circle.
Image credits: The National Police Air Service’s South West and Wales Region