The Tunguska event was a large explosion of between 3 and 50 megatons that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908.

The explosion over the sparsely populated East Siberian taiga felled a large number of trees, over an area of 2,150 km² (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died. The explosion is attributed to a meteor air burst, the atmospheric explosion of a stony asteroid about 50–60 metres (160–200 feet) wide.

The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s; 98,004 km/h (Mach 80). Though the incident is classified as an impact event, the object is thought to have exploded at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than hitting the Earth's surface, leaving no impact crater.

The Tunguska event is the largest impact event on Earth in recorded history, though much larger impacts are believed to have occurred in prehistoric times. An explosion of this magnitude would be capable of destroying a large metropolitan area. The event has been depicted in numerous works of fiction. The equivalent Torino scale rating for the impactor is 8: a certain collision with local destruction.

On 30 June 1908 N.S. (cited as 17 June 1908 O.S. before the implementation of the Soviet calendar in 1918), at around 7:17 a.m. local time, Evenki natives and Russian settlers in the hills northwest of Lake Baikal observed a bluish light, nearly as bright as the Sun, moving across the sky and leaving a thin trail. Closer to the horizon, there was a flash producing a billowing cloud, followed by a pillar of fire that cast a red light on the landscape. The pillar split in two and faded, turning to black. About ten minutes later, there was a sound similar to artillery fire. Eyewitnesses closer to the explosion reported that the source of the sound moved from the east to the north of them. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away.

The explosion registered at seismic stations across Eurasia, and air waves from the blast were detected in Germany, Denmark, Croatia, and the United Kingdom – and as far away as Batavia, Dutch East Indies, and Washington, D.C. It is estimated that, in some places, the resulting shock wave was equivalent to an earthquake measuring 5.0 on the Richter scale.

Over the next few days, night skies in Asia and Europe were aglow. There are contemporaneous reports of brightly lit photographs being successfully taken at midnight (without the aid of flashbulbs) in Sweden and Scotland. It has been theorized that this sustained glowing effect was due to light passing through high-altitude ice particles that had formed at extremely low temperatures as a result of the explosion – a phenomenon that decades later was reproduced by Space Shuttles. In the United States, a Smithsonian Astrophysical Observatory program at the Mount Wilson Observatory in California observed a months-long decrease in atmospheric transparency consistent with an increase in suspended dust particles.

Though the region of Siberia in which the explosion occurred was very sparsely populated in 1908, there are accounts of the event from eyewitnesses, and regional newspapers reported the event shortly after it occurred.