“Spring forward and fall back.” This statement’s relation to time is known the world over and holds significant meaning, especially, for countries practicing daylight saving time (DST). Daylight saving time represents an adjustment in time by moving forward one hour to increase the length of daylight in the evening, generally during the summer time. The practice is used for the summer because it robs one hour of daylight at the start of the day, rendering it impractical in winter. However, for people who follow the world clock, there is an added hour of daylight after regular work hours to engage in “daytime” activities of choice.

Records prove the use of daylight saving time for roughly 100 years but archaeologists have found evidence that earlier in human history, the sun’s schedule was the basis for developing daily schedules. In the year 1895, a New Zealand scientist George Vernon Hudson proposed a two-hour shift forward in October and back in March in a paper to the Wellington Philosophical Society. Despite interest in the idea, it wasn’t carried out. However, in the year 1908, DST was used in Thunder Bay, Ontario, Canada and on April 30, 1916, Germany became the first country to do a whole scale implementation of DST.

Among the benefits daylight saving time is said to bring are the conservation of energy and fewer traffic accidents due to the presence of natural light during the time when traffic on the road is heaviest.

To calculate the time zone an area theoretically falls in, the measurement of the area’s longitudinal coordinate is divided by 15.  GMT was the same as Universal Time up until 1972. It is now a simple time zone. In 1847, the British railroads accepted GMT as a standard. It was calibrated using telescopes. The Meridian, after which GMT is named, is used to represent 0 degrees longitude (although it is not truly 0 degrees). Every place on Earth is measured either in degrees east or degrees west of this line.

The fact that time zones around the world are all calculated as an offset or difference from standard time makes it easy to know the time of a place by just knowing the time zone it falls in and the standard time at the current moment. Calculations can also be done using local time once the expected time difference is known. Most time zones are exactly one hour apart and their time is calculated as an offset from Coordinated Universal Time you can see this in our time zone map or by using our time zone converter to check the time difference between one location and another. Heading west of the Prime Meridian / Greenwich Meridian, time is earlier while heading in an easterly direction time is later. The International Date Line adds 3 to the total of time zones around the world. Additionally, several time zones are 30 and 45 minutes apart. Therefore, there are more than the theoretic 24 time zones around the world.

Greenwich Mean Time (GMT) is so named, because the longitudinal line after which it is named passes through Greenwich, London. Although GMT and Coordinated Universal Time (UTC) share the same time there is a fundamental difference between them. GMT is a time zone. It is used by some African and European countries. UTC on the other hand is a time standard. It serves as the foundation for time zones worldwide. Hence no country officially uses UTC as its local time. They both remain constant and are not affected by daylight saving time (DST) although some countries observing GMT use DST in the summer.

UTC serves as the basis for civil time. This standard is maintained using extremely precise atomic clocks along with calculations of the Earth’s rotation. This standard is maintained, synchronized and coordinated worldwide. UTC is determined by International Atomic Time (TAI) and Universal Time. TAI is a combination of the output of 400 extremely precise atomic clocks that provides the precise calculation of the speed at which our clocks should tick. Universal Time is the time it takes the Earth to complete a turn on its axis and is used to validate TAI against an actual Earth day.