The skies in Zhoushan, China, turned blood red over the weekend, confusing locals and causing people on social media to declare an apocalypse.
The videos – taken on May 7 and spread on Chinese social media platforms Weibo and Sina – show confused onlookers gazing at the unusual sky. As apocalyptic as it might have looked, the explanation is a lot more to do with wavelengths than the end of times. According to the Zhoushan Meteorological Bureau, the glow was caused by the lights from fishing boats in the local port.
"When weather conditions are good, more water in the atmosphere forms aerosols which refract and scatter the light of fishing boats and create the red sky seen by the public," the bureau told Global Times.
Essentially, red wavelengths pass through the air more easily than blue ones, especially when it's foggy, when high pressure traps dust and small particles in the atmosphere, and when it's cloudy.
"A red sky appears when dust and small particles are trapped in the atmosphere by high pressure," explains the UK's Met Office. "This scatters blue light leaving only red light to give the sky its notable appearance."
Interestingly – as immortalized in the phrase "red sky at night, shepherd's delight, red sky in the morning, shepherd's warning" – this can sometimes be used as a way to forecast the weather.
In parts of the world where the weather systems move west to east, a red sky in the morning means that the area to the east is under high pressure, trapping small particles which are turning the sky red. This means that the area of high pressure has moved out to the east, in turn indicating that an area of lower pressure – maybe a cold front or rain – is on its way.
Meanwhile, if the sky is red at sunset, this means that the high-pressure area is on its way shortly, so you can expect a "shepherd's delight", or nicer weather.