Guests: Danny Baker, Jo Brand, Marcus Brigstocke
Air Date: 01 November 2013 at 10pm, BBC Two
XL Air Date: 03 November 2013 at 10.30pm, BBC Two
The least movement is of importance to all nature: the entire ocean is affected by a pebble.
Eratosthenes (276-194bc) of Cyrene was the Ancient Greek version of Renaissance Man. He was a mathematician, an astronomer, an athlete, a musician, a poet, the man who invented the term ‘geography’ and the first person to produce a map of the world with lines of latitude and longitude. His nickname was ‘beta’ – the second letter of the Greek alphabet - because he was second best in the world in almost every known discipline. His day job was chief librarian of the Great Library of Alexandria, the most important repository of knowledge in the classical world.
One of Eratosthenes’ most extraordinary achievements was to calculate the circumference of the Earth without leaving Egypt, using simple geometry. He knew that at noon on the summer solstice, in the town of Syene in southern Egypt, there was no shadow at the bottom of a well, indicating that the Sun was
directly overhead. Measuring the shadow cast by a stick planted in the ground in Alexandria at the same moment, he was able to determine that the Sun was at an angle of 7.2˚ from there. Conveniently, 7.2˚ is 1/50th of a full circle (50 x 7.2 = 360). So all he had to do to calculate the circumference of the Earth was to measure the distance between Alexandria and Syene and multiply it by 50.
Eratosthenes hired a slave to pace out the distance, and came up with 250,000 stades. We don’t know for sure which measurement of a stadion he used (there were several) but the 'walking' stadion was about 157.5 metres, and this gives an impressively accurate result: 39,690km, as against the modern measurement of 40,008km, so Eratosthenes was only 318 kilometres (198 miles) out – a 0.08% margin of error. The sums are even simpler in miles: it’s about 500 miles from Syene to Alexandria, and 500x50 = 25,000. The actual circumference of the Earth is 24,662 miles.
If the Earth's rotation suddenly stopped right now, nobody would get flung into space. Gravity would still be pulling us down onto the Earth and, in order to be flung into space, we would need to be travelling at a sufficient speed to overcome this force.
Doing the calculations shows that, in order to just be at the point where our rotational speed exactly overcomes gravity (i.e. the point where travelling any faster would cause us to leave the ground ever so slightly) we would have to be travelling at a speed of 17,686 mph. Currently, the Earth's maximum (i.e. at the equator) rotational velocity is a mere 1,041 mph. So, in order to fling us into space, the Earth would need to rotate 17 times faster than it currently does.
Natural selection actively favours slower snails, as these are the ones with the most energy leftover to spend on growth and reproduction. It is the first time that evolution has been shown to select for this trait in individuals of any species. The Chilean researchers behind this discovery measured the size of almost 100 garden snails (Helix aspersa). They also gauged their standard metabolic rate (a measure of the minimum amount of energy an animal needs in order to survive), by measuring how much carbon dioxide each animal produced while at rest. Then they released the snails.
After seven months, they recaptured them, also collecting the empty shells of those that had died. They found size did not predict which animals survived, but metabolic rate did, with surviving snails having a metabolic rate 20% lower than that of the snails that died. The lower each snail's metabolic rate, the greater its chance of survival. This indicates that nature is selecting for snails that are more energy efficient (and therefore slower).
Jason Manford, Sarah Millican and Bill Bailey join Stephen and Alan for a show about KEEPS. Will they keep it together? Will Alan keep any points? How do you get an ant to keep still? Tune in to find out!and NEXT WEEK...