The glow from the eruption of the Tonga volcano is visible even from Europe

When the sun sets tonight, look at the fading sky. If twilight turns purple, you may have noticed a "Tonga sunset". Heiko Ulbricht photographed this glow on January 21 in Grossopitz, Germany.

"A strong purple light appeared 26 minutes after sunset," says Ulbricht. "It could be aerosols from the eruption of the Hunga-Tonga-Hunga-Hapai volcano earlier this month."

Indeed, it may be so. On January 15, the volcano spewed 400 million kilograms of sulfur dioxide into the upper atmosphere, rising to a height never before observed by NASA satellites in Earth orbit. A huge cloud of sulfur aerosols passed over Australia and has since spread around the world through the stratosphere.

Purple sunsets may be a sign that these aerosols have reached you as well. Volcanic aerosols in the stratosphere scatter blue light, which, mixing with the usual sunset red, gives a purple hue.

But purple is not the only thing to pay attention to. In addition, sky watchers should pay attention to the bright yellow twilight arch, thin cloud structures in the arch and long purple rays. All these are potential signs of the "sunset of Tonga".