Meteor Day June 30 Meteor Day is celebrated on June 30, 2014. It commemorates the Tunguska event in 1908. The Tunguska event was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River at about 00:14 UT on June 30. The explosion is believed to have been caused by the air burst of a small asteroid or comet at an altitude of 5–10 kilometres (3–6 mi) above the Earth's surface. Different studies have yielded widely varying estimates of the object's size, on the order of 100 metres (330 ft). It is the largest impact event on or near Earth in recorded history.