A satellite image of Typhoon Hagibis.

(NOAA)

At a Glance

The phenomenon is caused by the "scattering" of sunlight.One Twitter user called it "creepy."Another said it looked like a "magic world."

As a massive storm like Typhoon Hagibis approaches landfall, you might expect foreboding dark clouds to appear on the horizon.

Instead, the sky turned a brilliant shade of princely purple in some places as Hagibis bore down on parts of Japan last week and into the weekend.

Photos posted to social media showed the surreal purple haze blanketing the sky. One Twitter user who captured the lightshow while leaving a train station called it a "magic world."

Another said "The purple sky is too creepy."

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The purple sky phenomenon is caused by changes in how sunlight is "scattered" by storm clouds and moisture in the atmosphere.

"Purple skies occur with many evening or morning thunderstorms – and typhoons," weather.com meteorologist Jonathan Belles explained. "You get the color of the sky through a process called scattering. The sun sends light to the earth in white, which gets scattered (or separated) into different colors depending on how much atmosphere that light goes through. The default is blue, which is why we usually see blue skies. At night, when the sun is lower on the atmosphere, that light gets more separated and we end up with purples and pinks. Throw in a lot of water from a thunderstorm or a typhoon, and that light has more things to bounce off of."

Purple skies in recent months are also related to a pair of volcanic eruptions that have put massive amounts of sunlight-scattering ash into the stratosphere. According to Sky and Telescope, the —from Raikoke in Russia’s Kuril Islands on June 22, and Ulawun in Papua New Guinea on August 3—each pushed dust and gases more than 11 miles high.

At such altitudes, the air is typically more stable, and volcanic ash can remain airborne for months or even years. Sunlight can reach the stratospheric ash just before sunrise and after sunset, helping enhance a purplish glow in the sky at these times.

Purple skies were seen last month as Hurricane Dorian passed the Atlantic coast of , as well as in last month and in Oregon this past weekend.

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