The explosion is believed to have been caused by the air burst of a large meteroid or comet fragment at an altitude of 5–10 kilometres (3–6 miles) above the Earth's surface. Different studies have yielded varying estimates of the object's size, with general agreement that it was a few tens of metres across.
The number of scholarly publications on the problem of the Tunguska explosion since 1908 may be estimated at about 1,000 (mainly in Russian). At around 7:17 a.m. local time, Tungus natives and Russian settlers in the hills northwest of Lake Baikal observed a column of bluish light, nearly as bright as the Sun , moving across the sky. About 10 minutes later, there was a flash and a sound similar to artillery fire. Eyewitnesses closer to the explosion reported the sound source moving east to north. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away. The majority of witnesses reported only the sounds and the tremors, and not the sighting of the explosion. Eyewitness accounts differ as to the sequence of events and their overall duration.
The explosion registered on Seismic stations across Eurasia. In some places the shock wave would have been
equivalent to an earthquake of 5.0 on the Richter scale
