A piece of sky fell on us

A piece of sky fell on us …….

The Event:

Around 7 in the morning on June 30^th 1908, people northwest of Lake Baikal observed a column of bluish light, nearly as bright as the Sun, moving across the sky. About 10 minutes later, a flash was also scene. And later …A piece of sky fell on the earth almost 100 years (June 30.1908) ago and devastated a region as big as a huge metropolis. This is the centenary year of the ravaging of Tunguska !

An artist's rendering of the flash ( by William Harman)

Siberia itself is a sparsely inhabited place. But region around the Tunguska river , could be called the Siberia of Siberia ! It is dammed lucky that nobody lived in that region. The explosion (about ~10-20 megatons)was larger than the effect of the bomb dropped on Hiroshima The estimate for this event is bout 50 such bombs . How big was the ‘ stone ‘ that was responsible for the disaster ?About 30-100 meters across! (Some of the estimates in literature are quite different) The explosion knocked over an estimated 80 million trees over about 2000 square kilometers. The earthquake from the blast measured 5.0 on the Richter scale . Many reindeer were killed.

Devastation of a forest by the event

Over the next few weeks in 1908, it seems night skies were aglow such that one could read in their light, from dust suspended in the the sky by the explosion. The observatories in America observed a decrease in overall light that lasted for several months, also from the suspended dust. A New Yorker article describes it in less prosaic terms: The night of the Tunguska explosion the skies were unnaturally bright across Europe—as far away as London people strolled in the parks past midnight and read novels out of doors while the sheep kept right on grazing and the birds stirred uneasily in the trees.

The Cause:

The solar system is a host to several marauders. These are objects which don’t stick to a particular path. The more important ones are the comets, asteroids and meteors . Everybody knows comets. Smaller rocks are termed meteorites, Asteroids are bigger boulders pebbles (ranging from a few meters thick to several thousand kilometers – these are termed as the debris left behind when the solar system was made) going around the Sun in an orbit in between that of Mars and Jupiter.

In general there is nothing to worry about asteroids. They just outinely encircle the sun. But occasionally one of these objects strays from its path because of a gravitational tug from another such object which could lead to a collision with the earth. When these objects come towards the moon , there is a direct hit on the moon causing the famous craters (ditches ) . However when tthey come towards the earth they have to encounter earth’s atmosphere. Most of them break up creating fireballs. The ensuing destruction is directly related to the size of the fireball. Craters are quite unlikely when these objects impact the earth.

It is believed that Dinosaurs were wiped out in a comet/asteroid impact of 65 million years ago. The culprit was probably a metropolis size object from t he sky. Direct impact is not the one which is responsible for large size destruction of the animals. There would , of course, be vast forest fires (as in Tunguska) which will destroy many animals. A vast quantituy of dust is thrown out into the sky which keeps the sunlight out for decades. This leads to severe cooling which slowly delivers the death blow. A lake CHICXULUB in Mexico has been seen at what could have been the impact point . The famous meteor crater ( also called Barrington crater) in Arizona was caused by an asteroid just 24 meters across about 20 – 50000 years ago. ! A similar crater which is a lake today is the LONAR crater in Aurangabad. .

The Lonar lake ( 1 km dia)

The opinion about the primary object which caused Tungusa depends on whether one is in New York or in Moscow. The Russians think it was a comet whereas the Americans believe that it was an asteroid. There are people who believe that it is due to an explosion of a UFO in air. Pieces of spacecraft has been found but it is said that they could be debris of some Russian space vehicle. There are also reports of a lake nearby which could have been due to the impact of the object from the sky

Such explosions are supposed to occur about once in a century. Much bigger ones are supposed to occur once in a millennium. If it had happened about 5 hours later the piece of sky would have hit the Russian(then) capital of St Petersburg and completely devastated the city. About 2 million people would have died . The Tsar with his whole retinue would have been eliminated and one wonders what would have been the future of Russia. Would the October revolution have taken place ? A youth called Vladimir Lenin would have continued living in Paris writing manifestos after manifestos!

( Thanks to the internet sites for the pictures)