Residents in the southern Russian city of Stavropol were left baffled earlier this week after a blinding light swept across the night sky before disappearing almost as suddenly as it started.
The noiseless flash, seen at about 9:30 p.m. on Monday, reportedly knocked out a number of street lamps and caused lights to flicker in some homes. The strange phenomenon was caught on a dashboard camera — in true Russian fashion — and has since been been widely shared on the Internet.
But despite global interest in the mysterious light, scientists and laymen alike are still no closer to knowing what caused the mysterious flash. The Moscow Times looks at some of suggestions put forward so far.
1. War Games
President Vladimir Putin announced Monday that 40,000 troops would this week take part in military drills across the country, in a show of the strength ahead of the first anniversary of Russia's annexation of Crimea, which was marked Wednesday.
Russia's top general later told the RIA Novosti news agency that the number of troops deployed was actually closer to 80,000 — and one possible theory is that the flash was caused by the use of rockets or ammunition during the staging of the military drills.
2. Northern Lights
Another theory is that the mysterious flash had something to do with the Northern Lights, which were visible over many parts Russia and Europe earlier in the week and produced some spectacular photos.
But while the lights were visible over Moscow and other parts of northern and central Russia, it is questionable whether they would have been seen as far south as Stavropol. The speed with which the flash appears and disappears could also put paid to this theory.
See the pictures: Stunning Polar Lights Over Moscow
3. Alien Invasion
Not convinced? Read on.
Just last year, a mysterious crop circle was recorded in the neighboring Krasnodar region. The 40-meter-wide marking appeared July in a local sunflower field, and some residents recalled seeing an unidentified object rising from the ground at the time, news site Svet Mayakov reported.
Read the story: Crop Circle Baffles Villagers in Southern Russia (Video)
4. Cloud-Measuring Device
Only in Russia, you may say. Yury Varakin, a meteorologist at the Stavropol Center, told ABC News that the flash was likely caused by a special high-powered projector lamp used by airports to measure the height of clouds. In fact European airports used to employ similar devices, but now use lasers instead.
5. Solar Eclipse
Could the flash be somehow linked to the solar eclipse, which took place on Friday and had Russians grabbing whatever they could to serve as a filter through which to observe the event?
In short, we are no closer to knowing what caused the mysterious flash, so why not watch the video and decide for yourself?