We still have to make sure that the time we define matches our everyday experience of day and night and the rhythms defined by the sun seen on Earth.
Every year, the time comes again when many of us switch our clocks from summer or daylight-saving time back to winter time. And the usual confusion sets in, is it an hour forwards or back? Why do we need to change the time at all? Indeed, EU member states have been asked if they would like to simply skip daylight saving time.
Historically, the sun has helped us tell time – but we’ve always had to make corrections to our readings for it to be effective.
The reason we have daylight saving time, for example, is the amount of daylight time isn’t consistent throughout the year – it’s different in the winter from what it is in the summer – and doesn’t always match our working days. But how has time-telling progressed throughout history and how good can it get?
Throughout the year the length of the days changes, as do the locations where the sun rises and sets on the horizon. There are also variations in the location and height of the sun during a day, with its peak height indicating that it’s midday.
Knowledge about these markers helped humans create the first sundials to tell time (by tracking shadows on the dial) thousands of years ago.
But time comes in many definitions. Using a sundial, you determine the local solar time at your geographical location. This varies a lot given that the Earth is a sphere.
If it’s midday in London, the sun is highest in the sky, but, simultaneously in New York it is much further to the east. As a result, longitude becomes important when comparing such times.
Even in the United Kingdom this difference amounts to 40 minutes when comparing the furthest locations east to west.
The longitudinal variation in solar time was used for navigation but it also caused a huge number of problems when establishing a rail network in 19th-century UK.
To ensure you knew when to expect a train, timetables needed to refer to a single time. At this point, a unified time was created to ensure all of the UK used what would become Greenwich Mean Time (GMT).
