QI: The Second Book of General Ignorance

by John Lloyd

  The word atmosphere is Greek for ‘globe of vapour’. Earth’s atmosphere is a succession of layers of gas, stretching about 100 kilometres (62 miles) into space. We live in the troposphere (tropos is Greek for ‘change’), which is warm and moist and is where all the clouds (except the noctilucent ones) form. At 11 kilometres (7 miles) up, the stratosphere starts (stratum is Latin for ‘covering’): it contains the protective ozone layer. The outermost layer is the mesosphere, somewhat confusingly called the ‘middle sphere’ because it’s between the other, inner layers and space. It starts nearly 5 kilometres (about 3 miles) up and is 32 kilometres (20 miles) thick. It’s too high for most aircraft and too low for space flight, and it’s nicknamed the ‘ignorosphere’ because we know so little about it.

  Noctilucent clouds form right on the boundary of the mesosphere and space. Clouds need water vapour and dust particles to form and the mesosphere is so dry and cold (about –123 °C) it was first thought that noctilucent clouds must be made of something other than water vapour. Now we know they are made of tiny ice crystals – a fiftieth of the width of a human hair – but we still don’t understand how they form.

  Another thing we don’t know about them is whether they have always existed or not. No one had ever reported seeing them until 1885 when they were first named by Otto Jesse, a German cloud enthusiast. This was just two years after the eruption of Krakatoa and at a time when the industrial age was at its peak. It seems that this was the first time dust had ever got high enough for clouds to form in the mesosphere.

  Today, the mesosphere is getting cooler still, as a result of increased carbon dioxide (CO2) emissions. At the same time, ironically, carbon dioxide is busy heating up the troposphere.

  CO2 naturally absorbs heat. In the thin air of the mesosphere, it simply sucks it up. But, in the troposphere, nearer the Earth’s surface, where the gases are more densely packed, CO2 collides continually with other substances (such as water vapour). This releases heat and causes global temperatures to rise and is known as the ‘greenhouse effect’.

  Over the past three decades, the number of noctilucent clouds has more than doubled, which has led some scientists to liken them to miner’s canaries: their eerie beauty warning of the dangers of climate change to come.

  How much does a cloud weigh?

  A lot.

  A popular unit of measurement for cloud-weight seems to be the elephant. According to the National Center for Atmospheric Research in Boulder, Colorado, an average cumulus cloud weighs about 100 elephants, while a big storm cloud tips the scales at 200,000 elephants.

  This is nothing compared to a hurricane. If you extracted the water from a cubic metre of hurricane, weighed it and then multiplied it by the number of cubic metres in the whole hurricane cloud, you would find that a single hurricane weighs 40 million elephants. That’s twenty-six times more elephants than exist on the planet.

  Which raises an obvious question: how can something that weighs as much as even one elephant float in the sky? The answer is that the weight is distributed across a vast number of tiny water droplets and ice crystals spread over a very large area. The biggest droplets are only 0.2 millimetre (less than 0.008 inch) across: you’d need 2 billion of them to make a teaspoon of water. Clouds form on top of updraughts of warm air. The rising air is stronger than the downward pressure of the water droplets, and so clouds float. When the air cools, and sinks, it begins to rain.

  In order to rain, the water in the clouds has to freeze before it falls. If the air temperature is low enough, it will fall as snow or hail; if not, the frozen drops melt on their way down. One puzzle is why there is so much rain in temperate climates like Britain, where clouds rarely get cold enough to freeze pure water. Catalysts like soot and dust help, providing nuclei around which ice can form, but there isn’t enough pollution of that kind to create all the rain.

  The answer seems to be airborne microbes. Certain kinds of bacteria are first-class ‘ice nucleators’, to the extent that they have the magical ability to make water freeze. Adding Pseudomonas syringae, for example, to water, makes it freeze almost instantly, even at relatively warm temperatures of 5–6 °C.

  The rain they ‘seed’ carries the bacteria to earth where they use their ice-making powers to mush up plant cells, including many crops, so they can feed on them. Air currents then sweep them back up into the atmosphere again, causing more rain.

  If this theory is right, the implications are enormous: merely growing the kind of crops that these ice-making bacteria like could wipe out droughts forever.

  How much of the Moon can you see from the Earth?

  It’s not half.

  Because the Moon takes exactly the same amount of time to revolve around its own axis as it does to orbit the Earth, we only ever see one face of it.

  But the Moon’s motion is not quite regular. As it goes round, it shifts backwards and forwards and side to side, revealing rather more of itself than half. This is known as ‘libration’, from the Latin librare, ‘to swing’, after the balancing movements of a pair of scales, or libra.

  Galileo Galilei (1564–1642) discovered it in 1637, and it comes in three forms.

  Latitudinal libration is caused by the fact that the Moon is slightly tilted on its axis. This means that from a fixed point on the Earth’s surface the Moon appears to rock first towards and then away from us as it passes by, allowing us to glimpse a little more of its top and bottom in turn.

  Longitudinal libration, or side-to-side motion, results from the fact that Moon travels round the Earth at a slightly uneven speed. It always rotates at the same rate but, because it’s travelling round the Earth in an ellipse rather than a circle, it’s going faster when it’s closer to the Earth and slower when it’s further away. We can see more of its trailing edge when it’s going away from us, and more of its leading edge when it’s coming towards us.

  Finally, there’s diurnal (‘daily’) libration. Because the Earth is also rotating on its axis, at different times of day we’re looking at the moon from a different angle. This allows us to see a bit round the back of the Moon’s western edge as it rises, and a bit more round the back of its eastern edge as it sets.

  The net result is that in any one month (each twenty-eight-day orbit of the Moon) we see 59 per cent of the Moon’s surface. The Soviet spacecraft Luna 3 took the first pictures of the ‘dark’ side of the Moon in 1959.

  The fact that the Moon always shows the same face to the Earth is known as ‘tidal locking’. Many of the 169 known moons in the solar system are synchronised in this way: including both the moons of Mars, the five inner moons of Saturn and the four largest of Jupiter’s moons, known as the ‘Galilean satellites’ after Galileo who also discovered them in 1610.

  Earth has a similar relationship with Venus. Despite spinning in the opposite direction to Earth, when Venus is closest to us (every 583 days) it always presents the same face. No one knows why. Astronomical bodies become tidally locked when they are relatively close to each other: Venus never gets nearer to us than 38 million kilometres (24 million miles). So it might just be chance.

  STEPHEN There is this strange thing called libration, which is like vibration beginning with an ‘l’. It was a thing that was noted by quite a few of the early astronomers …

  ROB BRYDON Can I say, sorry Stephen, but that’s not an acceptable way of defining a word: ‘Libration, it’s like vibration but beginning with an l.’

  What can you hear in space?

  In space, no one can hear you scream, but that’s not to say that there’s no noise there.

  There are gases in space, which allow sound waves to travel, but interstellar gas is much less dense than Earth’s atmosphere. Whereas air has 30 billion, billion atoms per cubic centimetre, deep space averages fewer than two.

  If you were standing at the edge of an interstellar gas cloud and a sound came through it towards you, only a few atoms a second would hit your eardrums – too little for you to hear anything. An extremel
y sensitive microphone might do better, but humans are effectively deaf in space. Our ears aren’t up to it.

  Even if you were standing next to an exploding supernova, the gases from the explosion would expand so rapidly that their density would decrease very fast and you’d hear very little.

  Sound doesn’t travel well on Mars, either: its atmosphere is only 1 per cent as dense as ours. On Earth, a scream can travel a kilometre (⅔ of a mile) before being absorbed by the air; on Mars, it would be inaudible at a distance of 15 metres (50 feet).

  Black holes generate sound. There’s one in the Perseus cluster of galaxies, 250 million light years away. The signal was detected in 2003 in the form of X-rays (which will happily travel anywhere) by NASA’s Chandra X-ray Observatory satellite.

  No one will ever hear it, though. It’s 57 octaves lower than middle C: over a million billion times deeper than the limits of human hearing.

  It’s the deepest note ever detected from any object anywhere in the universe and it makes a noise in the pitch of B flat – the same as a vuvuzela.

  How do you open a parachute?

  Not with a ripcord any more.

  The traditional way of opening a parachute was to pull a handle attached to a stainless steel cable known as a ripcord. Since the 1980s, pilot chutes, packed into a pocket in the parachute harness, have replaced ripcords. The pilot chute is much smaller than the main parachute – about a metre or 3 feet in diameter – and is usually released by the jumper pulling it out of its pocket and throwing it into the air. The sudden jerk as the pilot chute inflates removes the release pin for the main chute, which then opens. This is much safer than ripcords, as there is less chance of jamming.

  Modern parachute canopies aren’t shaped like jellyfish any more, either. They are rectangular and made of a double layer of parallel tubular cells, a bit like an airbed. The back and sides of each cell are closed, but open at the front. As the tubes fill with air, the canopy forms a wedge, similar to the shape of a hang-glider. And, just as with hang-gliders, parachutes can be steered. The control cords also allow the jumper to slow down or speed up the rate of descent.

  If the main parachute fails, there is a second or ‘reserve’ parachute to open and, even if the jump causes a loss of consciousness, there is an AAD, or Automatic Activation Device, which automatically releases the reserve parachute at about 230 metres (750 feet). The fatality rate for parachute jumps is one in 100,000, but almost none of these are caused by faulty equipment. Most result from reckless manoeuvres or from landing too fast; changes in wind conditions; or ‘canopy collisions’, where two parachutes get entangled.

  Modern parachutists descend at about 40 kilometres per hour (25 miles per hour). In freefall, a body’s terminal velocity – where air resistance prevents it from falling any faster – is about 200 kilometres per hour (125 miles per hour). In normal atmospheric pressure, and with an uncontrolled posture, it takes about 573 metres (1,880 feet) or 14 seconds to reach this speed.

  At higher altitudes, where the air is much less dense, a faster fall is possible. In 1960 US air force pilot Joseph Kittenger leapt from a balloon at 31,333 metres (102,800 feet) and reached a speed of 988 kilometres per hour (613 miles per hour), close to the speed of sound. Despite continuing to dive head first, he began to spin rapidly and blacked out, coming round when his chute opened automatically around 1.6 kilometres (a mile) above the ground. He is now helping skydiver Felix Baumgartner prepare to break his fifty-year-old record. Baumgartner plans to dive from a balloon at 36,500 metres (120,000 feet or 23 miles). He aims to reach a speed of 1,110 kilometres per hour (690 miles per hour). This will make him the first person to break the sound barrier outside an aircraft. No one knows what the physical effects of supersonic speed will be on a human body.

  Leonardo da Vinci is often credited with inventing the idea of a parachute, but the concept predates his famous 1485 drawing. An anonymous manuscript from a decade earlier shows a man wearing rather comical Italian dress and a nonchalant expression, holding on to a cone-shaped canopy. One can only hope it was never tested: it was much too small to slow his descent at all.

  STEPHEN I believe, Pam, that you felt some erotic feelings towards your instructor. Is that correct?

  PAM AYRES I did. I took a shine to the instructor. I think that’s why I jumped out the aircraft, really,’cause I wanted to impress him.

  JOHNNY VEGAS I often do that. If I like a woman, I jump out the window. Just to show ’em I really care.

  Why shouldn’t you touch a meteorite?

  It’s not because you might burn your fingers.

  A meteorite is an object that has fallen to Earth from space. Meteors, or ‘shooting stars’, are objects passing through the Earth’s atmosphere. Hundreds of tons of meteors bombard the Earth every day, but most of them are smaller than a grain of sand and burn up on entry.

  Both words come from the Greek for celestial phenomena, ta meteora, which translates literally as ‘things suspended high up’. In films and comics, meteorites are hot – they hiss and sizzle as they land in the snow. In reality, they’re usually cold: some are even covered in frost.

  This is because space is extremely cold. Although the friction of entering the atmosphere heats meteorites up, it also slows them down. They can take several minutes to fall to the ground: quite long enough for them to lose all the heat their outer surface has temporarily gained.

  Meteorites are either stony or metallic – metallic ones ring like a bell when struck with another piece of metal. Most of them are as old as the Earth itself. A few are found immediately after their fall, many have lain in the ground for tens of thousands of years before being discovered. You are most unlikely to come across one. In the whole of the USA between 1807 and 2009, only 1,530 verified examples were found – that’s fewer than eight a year. Actually seeing a meteorite falling, and then finding it, is even rarer. In the same period, it only happened 202 times – by coincidence, exactly once a year. The latest edition of the Natural History Museum’s Catalogue of Meteorites, published since 1847 and listing every known meteorite, records just twenty-four as ever being found anywhere in the British Isles. Meteorite experts get hundreds of calls from the public every year: they rarely turn out to be the real thing.

  The reason for not touching one is that you may contaminate any organic matter it might carry. If you do find a fresh one, you should put it in a sealed plastic bag (without touching it) and send it to your nearest research group.

  The ‘Bolton Meteorite’ was found in the backyard of a house in the high street of the Lancashire town in 1928. It caused great excitement, which was rather dampened by the verdict of the British Museum in London – that it wasn’t a meteorite at all, just a piece of burnt coal. Even so, it’s still on display at the Bolton Museum.

  When the first Europeans came to northern Greenland, they were amazed to find the local Inughuit, or polar Inuit, people using metal knives, despite having no idea how to either mine or smelt metal. They had chipped iron flakes off a meteorite using volcanic stones, and set them into handles made of walrus tusks.

  The meteorite was one of three that were the centrepieces of their religion. They were 4.5 billion years old and the largest weighed 36 tons. In 1897, the American explorer Admiral Robert E. Peary stole them, selling all three to the American Museum of Natural History in New York for $40,000.

  STEPHEN Around 50,000 meteorites larger than 20 grams fall from space to Earth every year. But more have been found on which continent than any other?

  RICH HALL Antarctica.

  STEPHEN Antarctica, yes.

  ALAN Bit tough on the penguins really, isn’t it.

  PHILL JUPITUS That’s why they always stand up, because there’s less of a surface area.

  What is a ‘brass monkey’?

  It’s got nothing to do with cannonballs.

  The phrase ‘cold enough to freeze the balls off a brass monkey’ is often said to refer to a metallic grid with circular holes in it, set u
nder a pyramid of cannonballs on a ship’s deck to keep it stable. When this ‘brass monkey’ got cold enough, the metal contracted and the cannonballs all popped out.

  In fact, the phrase means exactly what it says; the fake nautical euphemism is an attempt to make its rude humour more acceptable.

  First of all, it doesn’t make any sense to stack piles of cannonballs on the deck of a pitching warship. And they weren’t: they were kept in long thin racks running between the gunports, with a single hole for each cannonball.

  Second, these frames were called ‘shot-racks’ or ‘shot garlands’ and they were made of wood, not brass.

  Third, for one of these imaginary ‘brass monkeys’ to con tract even 1 millimetre (0.3 inch) more than the iron cannonballs it was supposed to hold, the temperature would have to drop to –66 °C, 8 degrees colder than ever recorded in Europe.

  Fourth, naval slang from the days of sail abounds in expressions that involve the word monkey, but the phrase ‘brass monkey’ is nowhere among them. The Sailors Word Book of 1867, the comprehensive dictionary of nautical terms compiled by the naval surveyor and astronomer Admiral W. H. Smyth (1788–1865), records monkey-block, monkey-boat, monkey-tail, monkey-jacket, monkey-spars, powder-monkey and monkey-pump (an illegal device for illegally sucking rum through a hole drilled in the cask). The only entry under brass reads: ‘BRASS. Impudent assurance.’

  Fifth, according to Dr Stewart Murray, a professional metallurgist and Chief Executive of the London Bullion Market Association, the difference in thermal contraction between brass and iron in such a situation is ‘absolutely tiny’, even at extreme temperatures, and ‘far too insignificant to have that kind of effect’.