In ancient times, human beings looked at the changing day and night patterns, apart from their ambient environment to chalk out their daily activities. They used sundials and hourglasses as the means to know the time, but this reading was fixed to a particular spot. As exploration, discovery and global trade increased, and the enormous scale of our planet was realised first-hand by those adventurous, the way time was perceived across regions began to change. With the Industrial Revolution, man became more inventive.
The expansion of transport and communication in the 19th century created a need for a unified time-keeping system, and time zones were introduced. The idea was proposed by Canadian engineer Sir Sandford Fleming, who in 1876 pioneered a worldwide system of time zones called ‘worldwide standard time’. The proposal divided the world into 24 time zones -- labeled A-Y (skipping J), each one covering 15 degrees of longitude.
Even today, the Earth has 24 time zones roughly of one hour each, with each zone covering 15° longitude.
A time zone is the local time of a region or country. There are different time zones around the world, with each region not experiencing the same time of day all at once. This means some people start their day, week, or new year before or after the rest of us, depending on where they are.
A simple reason why this is so is because the Earth rotates on its axis and moves about 15° every hour. After 24 hours (one day), it completes a full rotation. Confusion arises when we collectively work with people across geographies, or simply try to catch a flight to the other side of the world. Time zones have completely put such issues to rest, offering a rhythmic discipline to life.
Time work
Longitudes determine time zones. Longitudes are imaginary vertical lines that run on the surface of the Earth, dividing it into time zones. The Prime Meridian that passes through Greenwich, London, is the reference and other time zones are determined based on their distance from this point.
Greenwich Mean Time (GMT) is the standard time zone. Each 15° longitude west of this line is an hour earlier than that GMT, while each 15° east is an hour later. This can be calculated as -- The Earth rotates 360° in 24 hours, which means 15° an hour or 1° in four minutes. Thus, when it is noon in Greenwich, the time at 15° east of it will be 15 x 4 = 60 minutes, i.e., 1 hour ahead of GMT, but at 15° west, the time will be behind GMT by one hour.
Having different time zones enables most people around the world to experience the Sun during daytime hours. Another cue is that when the Sun is at the highest point in the sky, all the places along that longitude will experience midday or noon.
Meanwhile, countries have their own time zones, governed by policy or convenience. For instance, Russia, the largest country, boasts of 11 time zones, while both India and China, large nations in their own right, have decided to go with single time zones. India’s time zone is called Indian Standard Time (IST).
Do you experience days that get dark early on during some months of the year, and longer days with more daylight during other months? To counter this, a few countries adjust their time by an hour twice a year to make better use of the Sun during the day. This is called daylight savings time (DST).