According to the US Geological Survey, on the basis of the area of damage (600,000 square km or 231,660 square miles) and the area it was felt in (5,000,000 square km or 1,930,502 square miles) the largest known earthquakes in North America were the little-known Mississippi River valley earthquakes of 181112. They created new lakes and changed the whole course of the Mississippi. The area of strong shaking was ten times larger than that in San Francisco in 1906. Church bells rang spontaneously as far away as Ma.s.sachusetts.

It is impossible to predict when an earthquake will happen. One expert claims that the best way is to count the number of missing cats and dogs in the local newspaper.

Britain has up to 300 earthquakes a year but they are so small that the public notices only about 10 per cent of them.

What's the commonest material in the world?

a) Oxygen b) Carbon c) Nitrogen d) Water None of the above. The answer is perovskite, a mineral compound of magnesium, silicon and oxygen.

Perovskite accounts for about half the total ma.s.s of the planet. It's what the Earth's mantle is mostly made from. Or so scientists suppose: n.o.body has yet taken a sample to prove it.

Perovskites are a family of minerals named after the Russian mineralogist Count Lev Perovski in 1839. They may prove to be the Holy Grail of superconductor research a material that can conduct electricity without resistance at normal temperatures.

This would make a world of 'floating' trains and unimaginably fast computers a reality. At present, superconductors only function at unhelpfully low temperatures (the best so far recorded is 135 C).

Apart from perovskite, it is thought that the mantle is made from magnesio-wusst.i.te (a form of magnesium oxide also found in meteorites), and a small amount of shistovite (named after Lev Shistov, a graduate student at Moscow University, who synthesised a new high-pressure form of silicon oxide in his lab in 1959).

The earth's mantle sits between the crust and the core. It is generally a.s.sumed to be solid, but some scientists believe that it is actually a very slow-moving liquid.

How do we know any of this? Even the rocks spewed out of volcanoes have only come from the first 200 km (125 miles) below the surface and it's 660 km (over 400 miles) before the lower mantle starts.

By sending pulses of seismic waves downwards and recording the resistance they encounter, both the density and the temperature of the Earth's interior can be estimated.

This can then be matched to what we already know about the structure of minerals we do have samples of from the crust and in meteorites and what happens to these minerals under intense heat and high pressure.

But like much else in science, it's really only a highly educated guess.

STEPHEN What is the commonest material in the world What is the commonest material in the world?

CLIVE Jim Davidson's. Jim Davidson's.

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What does the Moon smell like?

Like gunpowder, apparently.

Only twelve people have walked on the moon, all of them American. Obviously, in their airtight s.p.a.ce suits the astronauts could not actually smell the Moon, but moondust is clingy stuff, and plenty of it was traipsed back into the cabin when they returned from the Moon's surface.

They reported that moondust feels like snow, smells like gunpowder, and doesn't taste too bad. The dust is actually mostly made of silicon dioxide gla.s.s created by meteors slamming into the Moon's surface. It also contains minerals like iron, calcium and magnesium.

NASA employs a small team to sniff every single piece of equipment which goes onto its s.p.a.ce flights. This is to ensure that no items which could change the delicate balance of the climate of the International s.p.a.ce Station make it on to shuttles.

The idea that the Moon was made of cheese seems to date from the sixteenth century. The first citation, from John Heywood's Proverbs Proverbs (1564), says 'the moon is made of greene chees'. It is thought that in this context, the word 'greene' means 'new', rather than having a green colour, as young cheeses would often have a more mottled appearance; much like the cratered Moon. (1564), says 'the moon is made of greene chees'. It is thought that in this context, the word 'greene' means 'new', rather than having a green colour, as young cheeses would often have a more mottled appearance; much like the cratered Moon.

Does the Earth go round the Moon or the Moon round the Earth?

Both. They go round one another.

The two bodies...o...b..t a common centre of gravity located about 1,600 km (1,000 miles) below the surface of the Earth, so the Earth makes three different rotations: around its own axis, around the Sun and around this point.

Confused? Even Newton claimed that thinking about the motion of the Moon gave him a headache.

How many moons does the Earth have?

At least seven.

Certainly the the Moon (or Luna, as astronomers call it) is the only celestial body to observe a strict orbit of the Earth. But there are now six other 'Near-Earth' Asteroids (NEAs) which do follow the Earth around the Sun, despite being invisible to the naked eye. Moon (or Luna, as astronomers call it) is the only celestial body to observe a strict orbit of the Earth. But there are now six other 'Near-Earth' Asteroids (NEAs) which do follow the Earth around the Sun, despite being invisible to the naked eye.

The first of these 'co-orbitals' to be identified was Cruithne (p.r.o.nounced Cru-een-ya Cru-een-ya, and named after Britain's earliest recorded Celtic tribe), a three-mile-wide satellite, discovered in 1997. It has an odd horseshoe-shaped orbit.

Since then, six more have been identified: the snappily named 2000 PH5, 2000 WN10, 2002 AA29, 2003 YN107 and 2004 GU and 2004 GU9.

Are they really moons? Many astronomers would say no, but they are certainly more than just run-of-the-mill asteroids. Like Earth they take roughly a year to orbit the Sun (think of two cars going round a race track at the same speed but in different lanes) and do, occasionally, come close enough to exert a very slight gravitational influence.

So whether you call them pseudo-moons, quasi-satellites, or companion asteroids, they are worth watching, not least because some or all of them may one day settle down into a more regular orbital pattern.

STEPHEN What man-made artefacts can be seen from the moon with the naked eye What man-made artefacts can be seen from the moon with the naked eye?

RICH Which moon are we talkin' about Which moon are we talkin' about?

How many planets are there in the solar system?

Eight. If you still think there's nine you've obviously been living in a parallel solar system.

On 24 August 2006, the General a.s.sembly of the International Astronomical Union finally agreed its long overdue definition of a 'planet'. Planets must fulfil three criteria: they have to orbit the sun, have enough ma.s.s to be spherical, and to have 'cleared the neighbourhood' around their orbit. Pluto only managed the first two, so was demoted to the status of 'dwarf planet'.

It's not perfect some astronomers argue that neither Earth, Jupiter or Neptune have cleared their orbits either but it does resolve the anomalous position of Pluto.

Even the planet's discoverers in 1930 weren't fully convinced of its status, referring to it as a trans-Neptunian object or TNO something on the edge of the solar system, beyond Neptune.

Pluto is much smaller than all the other planets, a fifth the ma.s.s of the Moon and smaller than seven of the moons of other planets. It isn't much larger than its own main moon, Charon (two more, smaller, Plutonian moons, Nix and Hydra, were discovered in 2005). Its...o...b..t is eccentric and on a different plane from the other planets, and its composition is completely different.

The four innermost planets are medium-sized and rocky; the next four are gas giants. Pluto is a tiny ball of ice one of at least 60,000 small, comet-like objects forming the Kuiper belt right on the edge of the solar system.

All these planetoid objects (including asteroids, TNOs and a host of other subcla.s.sifications) are known collectively as minor planets. There are 371,670 of them already registered, around 5,000 new ones are discovered each month and it is estimated there may be almost 2 million such bodies with diameters of over a kilometre. Most are much too small to be considered as planets but twelve of them give Pluto a run for its money.

One of them, discovered in 2005 as 2003 UB313 and now named Eris, is actually larger than Pluto. Others, such as Sedna, Orcus, and Quaoar, aren't far off. and now named Eris, is actually larger than Pluto. Others, such as Sedna, Orcus, and Quaoar, aren't far off.

Now Pluto, Eris and Ceres the largest body in the asteroid belt between Mars and Jupiter have been officially adopted as the first three dwarf planets.

This change isn't unprecedented. Ceres, like Pluto, was considered a planet from its discovery in 1801 until the 1850s when it was downgraded to an asteroid.

The American Dialect Society voted 'to pluto', meaning 'to demote or devalue someone or something' their Word of the Year for 2006.

ALAN [Pluto is] really, really big, and it goes around the sun! [Pluto is] really, really big, and it goes around the sun!

BILL Yes, well, so does my aunt Wilma. Yes, well, so does my aunt Wilma.

STEPHEN Yes, well, it's not really big at all. It's tiny. Yes, well, it's not really big at all. It's tiny.

ALAN Well, that's why it took so long to find it; don't be hard on it because it's small Well, that's why it took so long to find it; don't be hard on it because it's small ... ...

How would you fly through an asteroid belt?

Keep an eye open, but it's really unlikely you'll collide with anything.

Despite what you may have seen in bad sci-fi films, asteroid belts are typically quite desolate places. Busy when compared with the rest of s.p.a.ce, but desolate nonetheless.

Generally, the gap between large asteroids (ones which could do significant damage to a s.p.a.ce ship) is about two million kilometres (nearly 1 million miles).

Although there are some cl.u.s.ters called 'families' which have been recently formed from a larger body, it would not be too difficult to manoeuvre around an asteroid belt. In fact, if you picked a random course, you'd be lucky to see a single asteroid.

If you did, you might like to give it a name.

These days the International Astronomical Union has a fifteen-person Committee for Small-Body Nomenclature to control the naming of the ever-expanding roll-call of minor planets. It's not an entirely serious business, as these recent examples show: (15887) Daveclark Daveclark, (14965) Bonk Bonk, (18932) Robinhood Robinhood, (69961) Millosevich Millosevich, (2829) Bobhope Bobhope, (7328) Seanconnery Seanconnery, (5762) w.a.n.ke w.a.n.ke, (453) Tea Tea, (3904) Honda Honda, (17627) Humptydumpty, Humptydumpty, (9941) (9941) Iguanodon, Iguanodon, (9949) (9949) Brontosaurus, Brontosaurus, (9778) (9778) Isabelallende, Isabelallende, (4479) (4479) Charlieparker, Charlieparker, (9007) (9007) James Bond, James Bond, (39415) (39415) Janeausten, Janeausten, (11548) (11548) Jerrylewis, Jerrylewis, (19367) (19367) Pink Pink Floyd, Floyd, (5878) (5878) Charlene, Charlene, (6042) (6042) Cheshirecat, Cheshirecat, (4735) (4735) Gary Gary, (3742) Sunshine, Sunshine, (17458) (17458) d.i.c.k, d.i.c.k, (1629) (1629) p.e.c.k.e.r p.e.c.k.e.r and (821) and (821) f.a.n.n.y f.a.n.n.y Smith, Jones, Brown and Robinson are all official names of asteroids; so are Bikki, Bus, Bok, Lick, Kwee, Hippo, MrSpock, Roddenberry and Swissair.

Eccentricity in planet-naming isn't new. Pluto was named in 1930 by an eleven-year-old Oxford schoolgirl called Venetia Burney, whose grandfather pa.s.sed on her breakfast-time suggestion to his good friend Herbert Hall Turner, the Oxford Professor of Astronomy.

Perhaps 2003 UB313 will after all be named Rupert, Douglas Adams's name for the tenth planet in will after all be named Rupert, Douglas Adams's name for the tenth planet in The Hitch-hiker's The Hitch-hiker's Guide to the Galaxy Guide to the Galaxy. Stranger things have happened. The day before Adams suddenly died in 2001, the asteroid (18610) Arthurdent was first named. And now he has one of his very own: (25924) Douglasadams.

What's in an atom?

Mostly nothing. The vast majority of an atom is empty s.p.a.ce.

To get it into perspective, imagine an atom the size of an international sports stadium. The electrons are right up at the top of the stands, each smaller than a pin-head. The nucleus of the atom is on the centre spot of the pitch, and is about the size of a pea.

For many centuries, atoms, which were entirely theoretical, were thought to be the smallest possible units of matter, hence the word, which means 'not-cut' in Greek.

Then, in 1897, the electron was discovered, followed in 1911 by the nucleus. The atom was split and the neutron discovered in 1932.

This was by no means the end of the matter. The positively charged protons and uncharged neutrons in the nucleus are made of still smaller elements.

These even tinier units called quarks are given names like 'strangeness' and 'charm' and come not in different shapes and sizes but 'flavours'.

The distant satellites of the nucleus, the negatively charged electrons, are so odd they are no longer even called that but 'Probability Density Charges'.

By the 1950s, so many new subatomic particles (over 100) had been found that it was becoming an embarra.s.sment. Whatever matter might be, no one seemed able to get to the bottom of it.

Enrico Fermi, the Italian-born physicist who won the n.o.bel Physics Prize in 1938 for his work on atomic reactors, was quoted as saying: 'If I could remember the names of all these particles, I'd be a botanist.'

Since Fermi's time, scientists have settled on the number of subatomic particles inside an atom at twenty-four. This best guess is known as the Standard Model, giving the impression that we have a pretty good idea what's what.

The universe in general, as far as we can tell, is as underpopulated as the atom itself. s.p.a.ce, on average, contains just a couple of atoms per cubic metre.

Occasionally, gravity pulls them together into stars, planets and giraffes, which seems equally extraordinary.

STEPHEN Now, if the proton were the size of a drawing pin, the electron would be the size of a pinhead, and it would be one kilometre away. Now, if the proton were the size of a drawing pin, the electron would be the size of a pinhead, and it would be one kilometre away.

JEREMY HARDY Yeah, and if I were to put a pineapple on my head, I'd look like Carmen Miranda, but I don't! Yeah, and if I were to put a pineapple on my head, I'd look like Carmen Miranda, but I don't!

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What's the main ingredient of air?

a) Oxygen b) Carbon dioxide c) Hydrogen d) Nitrogen Nitrogen. As every twelve-year-old knows, it accounts for 78 per cent of the air.

Less than 21 per cent of air is oxygen. Only three hundredths of 1 per cent of the air is carbon dioxide.

The high percentage of nitrogen in the air is a result of volcanic eruptions during the formation of the Earth. Vast amounts of it were released into the atmosphere. Being heavier than hydrogen or helium it has stayed closer to the surface of the planet.

A person weighing 76 kg contains almost 1 kg of nitrogen.

Nitre is the old name for saltpetre, or pota.s.sium nitrate. A key ingredient in gunpowder, it is also used to cure meat, as a preservative in ice cream, and the anaesthetic in toothpaste for sensitive teeth.

For several hundred years, the richest source of saltpetre was the organic mulch that had seeped into the earth floor of human houses. In 1601, the unscrupulous activities of the 'Saltpeetermen' were raised in Parliament. They would break into houses and even churches, dig up the floors and sell the earth for gunpowder.

The word nitrogen means 'soda-forming' in Greek.

Beer cans with pressure-sensitive 'widgets' contain nitrogen, not carbon dioxide. The smaller nitrogen bubbles make a smoother, creamier head.

The only other significant gas in air is argon (1 per cent).

It was discovered by William John Strutt, Lord Rayleigh, who was also the first man to work out why the sky is blue.

Where would you go for a lungful of ozone?

Don't bother going to the seaside.

The nineteenth-century cult of healthy sea air was based on a fundamental misunderstanding. The bracing, salty tang has nothing to do with ozone, an unstable and dangerous gas.