On the night of September 2, 2025, reports of clouds sparkling in the sky above Mount Atago and other mountains as seen from Kyoto City were posted on social media one after another. At the time, there was no thunder in Kyoto City, and no fireworks displays were taking place. What exactly was glowing?
Around 7:00 PM on September 2, from an apartment in Shimogyo Ward, Kyoto City, clouds could be seen sparkling in the sky above Mount Atago to the northwest and the Higashiyama mountain range to the east. At the time, Kyoto City was clear, and no thunder could be heard. There were no fireworks displays or large-scale light-up events, and social media was flooded with posts questioning the nature of the light, with comments such as, "What's that glowing on the other side of the mountain?" and "Is it a sign of an earthquake?"
According to the Kyoto Regional Meteorological Observatory, the light in the night sky is believed to be thunder. Between 6pm and 9pm on September 2nd, developed cumulonimbus clouds passed over Fukuchiyama, Maizuru, and Kyotango cities in northern Kyoto Prefecture, causing thunderstorms. In addition to lightning strikes, a phenomenon known as "intracloud discharge" also occurred, in which lightning occurs only within the clouds, causing them to glow, and it is highly likely that this was visible from within Kyoto.
Maizuru and Fukuchiyama are approximately 60-70km from Kyoto, but because it is dark at night, lightning can sometimes be seen from clear areas.
