I was amused to read on the BBC News site ‘ Get ready for a cosmic surprise this autumn - Earth is about to get a second moon, according to scientists.’ I named my first science quiz book How Many Moons does the Earth Have? precisely because of this kind of silliness. My answer was ‘one’ and it still will be while a chunk of passing rock is briefly caught by Earth’s gravitational pull. Apart from anything, the suggestion that something is a moon just because it is briefly pulled off track by a planet’s gravity seems to reflect an underlying misunderstanding of how gravity works. Everything with mass distorts spacetime and causes moving objects to be displaced from their natural straight line path. This would make practically everything in space a moon if you took this argument to its limit, because they are all being pulled of track by the planets. The news item is also amusing because back in 2013, the TV show QI claimed that the Earth had a large number of moons (it was QI...