The explosions were heard in the early morning hours of June 30, 1908. It was a drama that has occurred countless times in Earth's history, and that is sure to play again.

Those Tungus tribesmen and Russian fur traders who happened to glance into the southeastern Siberian sky that fateful morning must have been startled to see a fireball streaking through the atmosphere toward their trading post of Vanavara and leaving a trail of light some 800 kilometers long. The object, whatever its nature, was approaching from an azimuth of 115 degrees and descending at an entry angle of 30 to 35 degrees above the horizon. Their gaze followed the bright fireball as it continued along a northwestward trajectory until it seemed about to disappear over the horizon. Then it shattered in a rapid series of cataclysmic explosions lasting about half a second over a distance of 15 to 20 kilometers.

The site was centered on 101 E by 62 N near the Stony Tunguska River 92 kilometers north of Vanavara. According to calculations, the object shattered at an altitude of 7.6 kilometers2 and became the first such cosmic visitor to strike Earth in the life time of civilized man.

According to an eyewitness in Vanavara:

"The sky split apart and a great fire appeared. It became so hot that one couldn't stand it. There was a deafening explosion [and my friend] S. Semenov was blown over the ground across a distance of three sazhens [six meters]. As the hot wind passed by, the ground and the huts trembled. Sod was shaken loose from our ceilings and glass was splintered out of the window frames."

What was this cosmic visitor?

Some have suggested it was a black hole. Others have wondered if it was a piece of anti-matter. A Japanese UFO group (Sakura), headed by Kozo Kowai, are convinced that it was the explosion of the nuclear power plant of an errant vehicle belonging to extraterrestrials. A number of science-fiction accounts have degraded the event to fantasy. Some critics hold that the entire history of nearly five decades of field work represents little more than a chain of mistakes. Most scientists disagree and point to a comet or an asteroid being the cosmic culprit.

What has been learned since the first organized investigation in 1927? And what is the current thinking?

To this day the vast Tunguska region remains a desolate area of mosquito-infested bogs and swamps amid the beautiful hilly taiga. To reach the epicenter you are dropped off by helicopter. Or you hike in.

For a trained eye, evidence of the blast is not difficult to identify, even after 90 years. The power of the blast felled trees outward in a radial pattern over an area more than half the size of Rhode Island. In the hot central region of the epicenter the forest flashed into an ascending column of flame visible several hundred kilometers away.

The fires burned for weeks, destroying an area of 1,000 square kilometers. Ash and powdered tundra fragments sucked skyward by the fiery vortex were caught up in the global air circulation and carried around the world. Meanwhile, bursts of thunder echoed across the land to a distance of some 800 kilometers.

The mass of the object has been estimated at about 100,000 tons and the force of the explosion at 40 megatons of TNT, 2,000 times the force of the atomic bomb exploded over Hiroshima in 1945. (By comparison, the explosive force of the Arizona asteroid that struck some 50,000 years ago, has been estimated at 3.5 megatons.

Following the Tunguska explosion, unusually colorful sunsets and sunrises caught the world's attention and were reported from many countries, including Western Europe, Scandinavia, Russia, and Western Siberia. The climax of visual displays occurred on the night of June 30th. Although they continued, they weakened exponentially over several weeks until they died away.

The New York Times of July 3, 1908 reported "remarkable lights" being "observed in the northern heavens on Tuesday and Wednesday nights." Scientists mistakenly attributed the dazzling displays to solar outbursts causing electrical disturbances in the atmosphere. Similar light displays had been reported in 1883 at the time of the Krakatoa volcanic explosion in the Sunda Strait, said the Times.

These "optical fireworks" and "light nights" were most prominent over Eastern Siberia and Middle Asia. They included a night sky bright enough to read a watch or newspaper by. Dust in the air at heights of from 40 to 70 kilometers caused high-altitude noctiluscent, or "night-shining," clouds that illuminated much of the visible sky. And there were halos around the Sun. A marked decrease of the air's transparency was recorded in the United States by the Smithsonian Astrophysical Observatory and California's Mount Wilson Observatory.

Disturbances in earth's magnetic field were reported 900 kilometers southeast of the epicenter by the Irkutsk Observatory. These were magnetic "storms" similar to the ones produced by nuclear test explosions in the atmosphere. The seismograph station some 4,000 kilometers west in St. Petersburg recorded tremors produced by the blast, as did more distant stations around the world.

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by Planetarium Director, Roy A. Gallant
Southworth Planetarium
University of Southern Maine