Every year, the time comes again when many of us change hours from summer or summer time back to winter. And confusion usually arises, is it one hour forward or backward? Why do we need to change time at all? Indeed, EU member states have been asked whether they only want to spend summer time.
Historically, the sun has helped us determine time – but we always have to make corrections to our reading so that it becomes effective.
The reason we have summer time, for example, is the amount of daytime is inconsistent throughout the year – different in winter and in summer – and does not always match our workday. But how do you manage time to develop throughout history and how well can it happen?
All year long the day changes, as does the location where the sun rises and sets on the horizon. There are also variations in location and altitude of the sun for a day, with peak height indicating that the sun is midday.
Knowledge of these markers helps humans create the first sundial that tells time (by tracking shadows on buttons) thousands of years ago.
But time comes in many definitions. By using a sundial, you determine the local sun time in your geographical location. This is very varied considering that the Earth is a ball.
If it's midday in London, the sun is highest in the sky, but, simultaneously in New York, it is far farther east. As a result, longitude becomes important when comparing such times.
Even in the UK this difference amounts to 40 minutes when comparing the farthest locations from east to west.
Longitudinal variations in solar time were used for navigation but also caused a large number of problems when building railroad networks in 19th-century England.
To make sure you know when to take the train, a schedule is needed to refer to one time. At this point, uniform time is created to ensure all UK uses what is going to be Greenwich Time (GMT). This idea was further developed to create a time zone that is now already established.
But the time zone seems to have been arranged rather randomly in several parts of the world. This is largely the result of the idea of uniting time in general trade and political territory.
For example, most European countries use central European time, although they easily cover three theoretical time zones. Spain adopted central European time during World War II under Franco's regime to harmonize the country closer to Germany. This remains today, despite the fact that the country covers exactly the same longitude as England.
The sun has also long been used to regulate the clock. To do that, only one instance in the time that needs to be marked: noon. This is achieved through the meridian sundial, which has small openings and north-south oriented lines, meridians. If the line is crossed, it is a local sun afternoon.
However, even this clever method needs to be corrected. The sun does not seem to move at constant speed across the sky.
The elliptical orbit of the Earth around the sun and the slope of the Earth's axis towards the orbital plane cause the sun to run above or below the average position throughout the year.
The time we actually use on our watch assumes a smooth and average sun position, so we call it "average solar time". This offset between two times is captured by the so-called time equation.
Then we began to arrange our clocks with visual cues, telegraph signals and then broadcast time signals via radio. Today we can use GPS to do it.
After realizing all the hassle of getting the right time from the position of the sun, the definition of time based on atomic clocks (International Atomic Time – IAT) seems perfect.
This is based on perfectly repetitive signals emitted by electrons in atoms when they change energy levels – allowing us to avoid depending on the position of the variable sun.
As a result, we should solve our problem about the right time – we can use an atomic clock instead of Greenwich Mean Time and just add it to the time zone.
But since 1972 we have included what is known as the second leap to maximize sunlight by calculating small deviations and slowing the rotation of the Earth when we measure Greenwich means solar time. This marks the slow mismatch between times as measured by atomic clocks and average solar time at Greenwich.
Leap seconds are introduced at the end of June or December as needed. This hourly inspection is carried out by the Earth International Rotation and Reference System Service.
This body uses radio telescopes that are connected together in very large distances to observe very distant objects known as quasars to measure the position and orientation of the right Earth.
Since 1972, we have added a total of 37 seconds at irregular intervals, which are quite a lot. This means relying on unsustainable atomic clocks. We will end the wrong half hour in 700-800 years – ultimately affecting when we want darkness.
So after all our efforts in finding the right time, examining the sun and making atomic clocks, we still rely on the sky. Instead of using the sun, we use distant radio sources in our universe that astronomers observe to tell us how much of our time differs from the perfect construction measured by atomic clocks.
In the end we still have to make sure that the time we set is in accordance with our daily experiences day and night and the rhythm determined by the sun seen on Earth.
And maybe it's good to keep thinking of time as a brother. If we want to live on Mars and its surroundings, we must make different times for days and years.
This article was republished from The Conversation by Daniel Brown, Lecturer in Astronomy, University of Nottingham Trent under a Creative Commons license. Read the original article.