As the title of this chapter implies, it is about the enigmatic concept of time – perhaps the least understood topic in physics. It is almost impossible to give a definition of time, and perhaps the most understandable was provided by the physicist John Wheeler, whose definition was ‘Time is nature’s way of preventing everything happening at once’!

Let us first discuss how astronomers measured the passage of time until the 1960s.

Local Solar Time

For centuries, the time of day was directly linked to the Sun’s passage across the sky, with 24 hours being the time between one transit of the Sun across the meridian (the line across the sky from north to south) and that on the following day. This time standard is called ‘Local Solar Time’ and is the time indicated on a sundial. The time such clocks showed would thus vary across the UK, as noon is later in the west. It is surprising the difference this makes. In total, the UK stretches 9.55 degrees in longitude from Lowestoft in the east to Manger Beg in County Fermanagh, Northern Ireland, in the west. As 15 degrees is equivalent to 1 hour, this is a time difference of just over 38 minutes.