The Science of Discworld IV

the same problem concerning our planet, and that did not stop scientists pinning down its shape and size. Also how old it is, although the accepted scientific figure for the age of the Earth remains contentious in some quarters because some people don’t like the answer, and of course that is all you need to prove it must be wrong.
    The ancient Greeks started out thinking the world was flat, but they revised their opinion when they began to appreciate indirect evidence to the contrary. Like several earlier cultures, they were aware that the Moon is a sphere. Superficially, it may look like a flat disc viewed sideways on, but because of its phases, simple geometry reveals that it must be roughly spherical. The Sun, which is difficult to look at without blinding yourself, is a disc that seems to be almost exactly the same shape and size as the Moon, so presumably that,too, is a sphere. Eventually the Greeks concluded that the Earth is a sphere as well – a bit of a surprise because it doesn’t look like one. If you live in mountainous regions the world looks bumpy; if in a desert, away from big sand dunes, it looks flat. But if you look really carefully, you will see ships slowly disappearing below the horizon as they leave harbour, so the
sea
is curved. Other clues, such as the Earth’s shadow on the Moon during an eclipse, also indicate that the Earth is round. To the Greek worldview, a mix of human-centred and universe-centred thinking, that made narrative sense: a sphere is a perfect geometric form, so of course the gods would have used it to make the world.
    After 250,000 years or more of the evolution and cultural development of modern humans, preceded by millions of years of our hominin ancestors, we have developed our own kind of narrativium, in which things happen because we tell each other stories about them, and then become inspired to
make
them happen. Having told ourselves innumerable stories about the shape of the Earth, most of them wrong, we have finally managed to gain a pretty accurate picture of the shape of our home planet. It is, as previously mentioned, a potato. The potato is very close to a spheroid of rotation, like a beach ball that someone has sat on. A spheroid is not too far away from a sphere. The Greeks did an amazing job for their time.
    A spherical shape makes even more sense once you realise that we live on a planet that is similar to the other planets of the solar system, and once you have telescopes revealing that Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune (not to mention Pluto, Ceres, Titan, and many other bodies that are not classed as planets) are round. As above, so below. However, all this relies on logical inference, and it is only relatively recently that we have possessed the technology to look at the Earth from outside. The famous ‘Earthrise’ photo taken from lunar orbit in 1968 by astronaut William Anders ofApollo 8 shows a gibbous Earth, predominantly blue and white but with shades of green and brown, rising above a sterile, grey, mountainous lunar landscape. (The first manned lunar landing, Apollo 11, happened a year later.) This image dramatised our world’s fragility as it sailed through space, forever changing the associations of the word ‘Earth’. Ironically, the astronauts weren’t supposed to have taken it. NASA transcripts include an exchange between Anders and mission commander Frank Borman, who had previously taken a black and white photo of the Earth rising:
    Borman
: Oh my God! Look at that picture over there! Here’s the Earth coming up. Wow, is that pretty!
    Anders
: Hey, don’t take that, it’s not scheduled.
    Borman
: You got a colour film, Jim? fn2
    Anders
: Hand me that roll of colour quick, will you!
    The rest was a triumph of astronautical narrativium over managerial mission schedules.
    Even though we now know the world is round, some diehards still refuse to accept the evidence. They ‘know’ that the Moon landings never happened; they were all faked in Hollywood studios. There is no question that this is possible
now
; movie-makers routinely use computer-generated imagery to create far more complicated things – among them the movie
Apollo 13
, made 25 years later, with highly realistic special effects. It’s doubtful that the imagery existed
then
, but of course secret guv’mint projects were concealing technological advances that they only made public much later … Though not, apparently, the relatively