Can clouds predict earthquakes? YouTube has footage of strange multicoloured clouds seen just before the recent earthquake struck Sichuan province in China.

The first impression is of a rainbow smeared on to small scraps of clouds, a phenomenon best known in a circumzenithal halo. This is created when sunlight shines through cirrus clouds full of tiny hexagonal ice crystals shaped like plates. The crystals behave like glass prisms, splitting the light into a bow with the colours of the spectrum, often brighter than a rainbow.

But one puzzle is that the colours in the Chinese clouds were upside down from a normal circumzenithal halo - red pointing towards the horizon and blue towards the Sun, instead of the other way round.

Is there a way to predict earthquakes? For centuries people have reported seeing fogs before earthquakes strike, or electrical flashes and strange lights. But reliable earthquake prediction has proved elusive, although one feature of the Earth's atmosphere offers hope.

Earthquakes are sometimes heralded by changes in the ionosphere, the Earth's upper atmosphere on the edge of space.