On November 30, 2017, two Taiwanese scientists claimed to have recorded the longest rainbow in history. Chou Kun-hsuan and Liu Ching-huang, both professors from the Department of Atmospheric Science at the Chinese Culture University (CCU), in Taipei, filmed the phenomenon, which lasted longer than they imagined: eight hours and fifty-eight minutes, exactly.
According to Chou, the rainbow started at 6:57 a.m. and lasted until 3:55 p.m., which is truly surprising given that rainbows typically last about fifteen minutes. For this reason, it was included by the Guinness Book of Records as the longest rainbow, taking the position from the one produced in March 1994 in the United Kingdom, with six hours of duration.
Capturing this world record was not among the teachers’ plans. Originally, they were observing the rainbow to demonstrate an academic hypothesis : that it descends seven degrees every thirty minutes. But that day, researchers found themselves observing the phenomenon for much longer than anticipated.
Initially, it was not a single rainbow, but four. Chou stated that there were four rainbows, including two primary rainbows combined with two supernumerary rainbows.
How could a rainbow last so long? According to researchers for the newspaper Taiwan News, the culprit would be a seasonal monsoon blowing from the northeast; This meteorological phenomenon trapped moisture in the air, a moisture that formed clouds and constant light rain. This rain, in turn, partially covered the sky. In fact, the university’s weather station measured the wind moving at a relatively slow rate: two to five meters per second, thus prolonging the ideal conditions for the appearance of rainbows.
How is a rainbow produced?
Centuries ago, Newton observed the phenomenon of the refraction of light: when light passes from one medium to another, for example, from air to glass, the beam of light decomposes into seven vivid colors ; something similar happens during the rainbow phenomenon, when sunlight falls, this time, on raindrops.
This breakdown of light occurs in the human visible spectrum. This leads us to think that, despite the fact that the rainbow is a physical phenomenon, it is nothing more than an optical effect, perceived by the capabilities of the human eye, which in turn remains ‘blind’ to other phenomena in non-visible spectra.
