Tuesday 24 July 2012

Out of this World Again

In an era when few people would have travelled more than a 1000-miles from their place of birth, the Greeks and Romans could still get their heads around vast distances. By the First Century AD time the popular belief was that some clouds reached a height of 103-miles above the earth's surface (the very highest actually only reach 53-miles). But 100-years earlier, Posidonius of Rhodes (even though he was born in Syria) was far more conservative when he concluded that clouds and winds were only five miles high - his calculation is very close to the maximum height of the Troposphere, where most clouds do exist. His other number crunchings were also much more accurate than his contemporaries. In 90BC he estimated the Sun's enormous diameter, and in doing so realised the vast distances of space. He reasoned the moon was 230,000-miles from the earth (it actually varies between 237,600-miles and 271,100-miles) and from the Moon to the Sun was 575,000-miles. Pythagoras had previously produced a distance of only 29,000-miles. The actual distance is 93-million miles, so they were both a little out, but when all said and done, in a time when most people measured a long way as the next town, Posidonius realised there was a whole lot more beyond the horizon.

Find out if Calvus could count that far 

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