We name a direction after the clock, but the clock is thought to have borrowed it from something older: the shadow of a stick in the sun. Across most of the northern hemisphere, a sundial's shadow sweeps the same way clock hands do. Across most of the southern hemisphere, it runs the other way.

That earthy smell when rain hits dry ground has a name, coined by two Australian scientists in 1964: petrichor. Behind it sit three layers of explanation. An oil held in rocks and soil, a compound made by soil bacteria that seems to work as an advert, and raindrops that may fling the scent into the air with tiny bursting bubbles.

You walk into the kitchen with purpose and stop dead. What was I here for? Psychologists have tested this in virtual rooms and real ones, and found that passing through a doorway can make people worse at remembering what they had in mind. The likely culprit is the way the mind files life into episodes. Though, as later studies show, the effect isn't as reliable as it first looked.

A rising full Moon can look enormous, and an hour later, high in the sky, ordinary again. A camera shows it hasn't changed size at all. People have puzzled over this for more than two thousand years, and scientists still don't fully agree why.

Ask why the sea is blue and most people will say it mirrors the sky. Reflected skylight is part of what you see, but the deep blue comes from the water itself. Water is faintly blue, because it soaks up red light. And the reason it does that may make water's colour unique in nature.