Original sentence: It is known most prominently for what has become known as The Tunguska Event, an enormous impact event near the  Stony (Podkamennaya) Tunguska River at about 7:17 AM local time, on the morning  of June 30, 1908.Numerous hypotheses and conspiracy theories about UFOs and other phenomena have been suggested over time and persist today.The conventional explanation is that it was caused by the explosive disintegration of a stony asteroid about 60 metres (~200 feet) across at an altitude of about 8 kilometres (~5 miles), but some contest that there are many things not explained by this theory.The explosive power neccessary for such an enormous radius of effect has been calculated to have been within the range of 10 to 15 megatons of TNT (40 to 60 petajoules).This event is peculiar in that while it felled an estimated 60 million trees over 2,150 square kilometres, it did not leave a crater.Witnesses claim they felt the impact as far away as 1,000 kilometres (600 miles), and as far as 500 kilometres (300 miles) away some claimed to have heard a 'deafening bang' and to have seen a cloud on the horizon
Edited sentence: At 500 kilometres, witnesses claimed to have heard a 'deafening bang' and to have seen a cloud on the horizon.It is known for an enormous impact event near the  Stony (Podkamennaya) Tunguska River at about 7:17 AM local time, on the morning  of June 30, 1908, which felled an estimated 60 million trees over 2,150 square kilometres but did not leave a crater.Numerous hypotheses about UFOs and other phenomena have been suggested over time; for more details, see the article on the Tunguska event.The conventional explanation is that it was caused by the explosive disintegration of a stony object about 60 metres across at an altitude of about 8 kilometres, but there are many things which are not explained by this theory.The impact was felt as far away as 1,000 kilometres.The size of the blast is said to have been the equivalent of between 10 and 15 megatons of TNT (40 to 60 petajoules)