Who came up with the concept of time?

The early people probably began to wonder about passing of time from observing natural phenomena such as sunrise and sunset, the waxing and waning of the moon, and cycle of birth, growth and death of all living things. This led to the concept that events may take place in a sequence, and there were certain intervals between these events. Archaeological findings dating back 60,000 years showed that people then already had a concept of past, present and future. As civilisations progressed, more and more precise time measuring systems were developed in various cultures to mark the increasingly complex events in their daily lives, as well as to explain the relationship between man and the universe in a spiritual way.

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How long is 1 second?

An average person’s heart beats about 70 times a minute. So, the duration it takes from one heartbeat to the next is slightly less than one second. We, of course, have to measure the second more precisely than that. Scientists used to do this by measuring duration of a day, or a year, through astronomical observations – that is observing distant stars. The duration is then divided by a large number – 86,400 if it’s a day, or about 31 million if it’s a year – to give a second. Now, scientists use what is known as atomic clocks to generate the second. An atomic clock is based on the oscillation of some caesium atoms. They are so accurate that the time derived from them will stay within one second in almost a million years.

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Who decided on ‘seconds’, ‘minutes’ & ‘hours’ to measure time?

These units of time evolved through many generations of ancient cultures such as the Egyptians, the Babylonians and the Greeks, and were later adopted throughout the world.

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Why there are 24 hours in a day and not more or less?

The ancient Egyptians used the rising and setting of certain stars as markers in their calendar. In doing so, they observed that during any night, the rising of these stars occur at regular intervals such that the night could be roughly divided into twelve equal parts. Later, daylight was also divided into twelve equal parts to follow the night, which gave our day twenty-four hours.

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Why must 60-second make 1 minute and 60 minutes make 1 hour, not the other way round?

Subdivisions of the hour probably have their origin in ancient Babylon. The Babylonians developed a number system called Sexagesimal around 4,000 years ago. Sexagesimal is based on 60. The system that we are more familiar with is the decimal system, which is based on 10. The Babylonians found that, in astronomy, Sexagesimal was far superior to the other systems, and it was later adopted to subdivide the hour into 60 minutes, and the minute into 60 seconds. Through the ancient Greek Empire, this system gained acceptance in the Mediterranean cultures and later spread throughout the world. It is still in use today, not only in time but also in angular measurements.

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Where did the “o’clock” come from?

The “o” is the abbreviation “of”, and “o’clock” is to tell the “number of clock”.

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What’s ‘a.m.’ and ‘p.m.’?

“a.m.” came from Latin words “ante meridian”, which means “before midday” or “before noon”. It is the portion of the day between midnight and the following noon.
“p.m.” came from Latin words “post meridian”, which means “after midday” or “afternoon”. It is the portion of the day between noon and the following midnight.

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How is time measured?

Any measurement of time is based on counting the cycles of some phenomenon that repeats itself regularly, and then accurately measuring fractions of that cycle. One example is the rotation of the earth on its own axis, which gives the cycles of days and nights. Each cycle is then divided into hours, minutes and seconds. Standard for time is now provided by the natural frequencies of oscillations of atoms. An atomic clock provides the second by counting the cycles of oscillations of caesium atoms.

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What is a global positioning system (GPS)?

Global Positioning System, or commonly known as GPS, is a satellite based navigation system operated by the US Department of Defense. GPS satellites broadcast signals that contain information on position and time. Anyone with a GPS receiver can find out his/her position anywhere on the surface of the earth quite accurately. For timekeepers, GPS satellites provide useful means of comparing time since they also carry on-board atomic clocks.

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What is Singapore Standard Time? How is SST determined? How is the accuracy of SST assured?

SST is an abbreviation of Singapore Standard Time. It is obtained by offsetting +8 hours from UTC. The National Metrology Centre maintains the caesium atomic clocks. They are regularly compared, through GPS satellites, with some 260 atomic clocks maintained in about forty countries around the world. An international organisation BIPM (Bureau International des Poids et Measures) collects data of these atomic clocks and computes the world average time, or international time. Singapore Standard Time is then generated by aligning our caesium clock to this international time and corrected for the time zone of Singapore. Consequently, UTC of Singapore is within the accuracy of 100 nanoseconds (one-billionth of a second) from UTC at any time.

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How many time zones are there in the world?

Our day has been divided into 24 hours. The world is therefore divided into 12 time zones in the Eastern Hemisphere and 12 in the Western Hemisphere.

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How do they decide what time it is anywhere in the world?

The international organisation BIPM continuously calculates the world average time from the 260 atomic clocks in forty countries. The resulting international time is called the Co-ordinated Universal Time. Correcting the Co-ordinated Universal Time for the time zone gives the time of that location. For example, Singapore is in the eight-hour time zone. So, adding eight hours to the Co-ordinated Universal Time is the Singapore Standard Time.

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Why is it so important to get the right time?

In our everyday life, we need to have a common time reference so that we can co-ordinate our activities. For example, we start school or work at a given time. Buses and MRT have to run on schedule. Planes and ships have to arrive and depart at the ports at specific time. Time is also critical in transactions at the banks and stock exchanges. Businesses are now done through the Internet, which also requires correct time.

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What is GMT?

GMT, representing the acronym of “Greenwich Mean Time”, is the mean solar time at the meridian of old observatory in Greenwich, England, the time standard against which all other time zones in the world are referenced. It is the same all year round and not effected by Summer Time or Daylight Savings Time. GMT was originally set-up to aid naval navigation when the globe started to open up with the discovery of the "New World" (America) in the fifteenth Century. Sometimes GMT is referred to as Z ("Zulu"). This arises from the military custom of writing times as hours and minutes run together and suffixed with a single letter designating the time zone: 2100Z = 21:00 UTC. The word "zulu" is the phonetic word associated with the letter "z". GMT is a historic term, which is in a strict sense obsolete, though often used as a synonym for UTC, e.g., BBC still uses this abbreviation for patriotic reasons. However, GMT was not derived from atomic time and had no leap seconds, it now has no clear meaning and was replaced by Universal Time (UT) in 1928. Today, GMT is still in use in some fields like emails, cookies and US space shuttle. It is still used as the UK's civil time. In fact, no clocks read GMT. BBC and telephone time signals in the UK and worldwide have broadcast UTC since 1972. The British set their clocks to UTC, not GMT.

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What is UT?

UT (Universal time) indicates the mean solar time on the Greenwich meridian beginning at midnight. It is defined by the Earth's rotation and determined from astronomical observations. Accordingly, the day was divided into 86400 seconds. This establishes a connection between second, the scientific unit of time, and the Earth's rotation. This time scale is slightly irregular. There are several different definitions of UT, but the difference between them is always less than about 0.03 s. Usually one means UT2 when saying UT. UT2 is UT corrected for pole wandering and seasonal variations in the Earth's rotational speed.

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What is UTC?

UTC is the acronym of “Coordinated Universal Time”. As UT is affected by the motion of the earth's rotation pole, UT1 corrected for this effect was in use. However, UT1 is still not a uniform time scale. The variation in UT1 is dominated by seasonal oscillations due to the irregularity of the earth's rotation. In an effort to derive a more uniform time scale, scientists established UT2 by applying an adopted formula deducting the seasonal oscillations. Unfortunately, UT2 is also not a uniform time scale due to other variations including tides and winds and the exchange of angular momentum. So rather than base time keeping on the rotation of the earth, we now use Atomic Time, time based on atomic measurements. Thus time scale based on the atomic second but corrected every now and again to keep it in approximate synchronisation with the earth's rotation is called UTC. The correction is known as the leap second. The abbreviation UTC can be followed by an abbreviation of the organisation that publishes this time reference signal. For example, UTC(USNO) is the US reference time published by the US Naval Observatory, UTC(PTB) is the official German reference time signal published by the Physikalisch Technische Bundesanstalt in Braunschweig and UTC(BIPM) is the most official time published by the Bureau International des Poids et Mesures in Paris, however UTC(BIPM) is only a filtered paper clock published each year that is used by the other time maintainers to resynchronise their clocks against each other. UTC is an “average world time” calculated by the BIPM from the readings of more than 200 atomic clocks located in metrology institutes and observatories in more than 30 countries around the world. Singapore is also part of this network and UTC(SG) is the Singapore version of UTC. All these UTC versions do not differ by more than a few nanoseconds.

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What is TAI?

TAI, (Temps Atomique International = International Atomic Time), is a uniform and stable time scale defined by the same worldwide network of atomic clocks that defines UTC. The unit of Atomic Time is the atomic second and was defined by the following description in October 1967: the second is the duration of 9192631770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of casium-133 atom without the influence from magnetic field. According to the definition, any long time interval should be the accumulative sum of the seconds. TAI is formed not from a world clock in Paris, but from the combined readings of more than 260 atomic clocks worldwide. In contrast to UTC, TAI has no leap seconds. UTC is identical with TAI except that from time to time a leap second is added to ensure that the Sun crosses the Greenwich meridian at noon UTC to within 0.9 second when averaged over a year.

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What is a leap second?

UTC based on atomic time is a uniform time scale and 86400 seconds define the length of a nominal day. UTC is kept closely in line with the rotation of the Earth. But because of the variations in the earth's spin the length of the actual day can be shorter or longer than the nominal day of 86400 seconds, this causes UTC to depart by more 0.9 seconds from UT1. Leap second is therefore introduced and added to make the step correction in order to bring UTC back into line. Leap seconds are usually inserted after the 60th second of the last minute of December 31 or June 30.

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What is the time delivered by a GPS receiver?

Navstar GPS (Global Positioning System) is a satellite based navigation system operated by the US Department of Defense. The signals broadcast by GPS satellites, contain all information required by a GPS receiver in order to determine both UTC and TAI highly accurately. Commercial GPS receivers can provide a time reference that is closer than 340 ns to UTC(USNO) in 90% of all measurements, classified military versions are even better.

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What is a cesium atomic clock?

A cesium atomic clock is a device that uses as a reference the exact frequency of the microwave spectral line emitted by atoms of the metallic element cesium, in particular its isotope of atomic weight 133. It uses the exquisite reproducibility of spinning atoms of the element cesium. The integral of frequency is time, so this frequency, 9,192,631,770 cycles/second, provides the fundamental unit of time, second. Cesium atomic clock is the world's best timekeepers.

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Is there a difference between time referenced to UTC and to GMT?

UTC is the modern successor of Greenwich Mean Time. Or we can say UTC is atomic time while GMT is the earth rotation time. Their difference is less than 0.9 second.

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If the difference is insignificant, why is there a need to change?

UTC is the modern-day reference established and adopted under international agreement. GMT is an archaic system and is no longer used. As Singapore’s economy becomes more global, there would be implications for time-sensitive information exchange, especially on the Internet. Potential legal disputes regarding a difference in reference point could be avoided if Singapore referenced itself to the international norm. Furthermore, with the adoption of UTC, the reference for Singapore Standard Time would now reside in Singapore (as part of the international network) instead of in Greenwich.

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How is the national time linked to 1711?

The National Metrology Centre is now working with SingTel to look into the way that 1711 time announcement service links to the SST. We are trying to provide SingTel the dedicated time signal to 1711 for the traceable time service.

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Swatch has recently launched an Internet time. How would this affect the
launch of SST?

Swatch Internet Time is a time specially defined by Swatch Watch Company. A day is divided into 1000 “beats”, each equivalent to 1 minute 26.4 second. 000 Swatch Internet Time is midnight in Biel, the home of Swatch (= UTC+1hr). It claims that a line of Swatch watches keeps the Swatch Internet Time, purportedly to help coordinate international chat sessions. It is a special time for Swatch watches, differentiated from the general meaning of time service through Internet. There is no clear need for Swatch Watch Company to introduce Swatch Internet Time.

SST is a time in general meaning, everyday used in Singapore, equivalent to UTC plus 8 hours time zone difference.

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Is there an authority on Singapore time? How is time in Singapore set at present?

Currently time services in Singapore are available through the Time Announcement Service of Singapore Telecom (telephone number 1711) as well as through television broadcasts provided by the Television Corporation of Singapore (TCS). These are widely used by industry and public at large to synchronise their clocks and watches. However these time signals are not formally linked to a nationally or internationally recognized time scale. Both SingTel and TCS also do not regard themselves as the national authority for disseminating the correct time scale.

As the national measurement authority, NMC (National Measurement Center) has established the national time scale using an ensemble of caesium atomic clocks. These clocks are continuously compared with the international time scale through the satellite system of the Global Positioning System (GPS). Our time data are sent to the International Bureau of Weights and Measures (BIPM) as part of an international network which contributes to the generation of the international time scale ¾ Coordinated Universal Time (UTC).

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How/in which areas is Singapore time used?

The world is divided into a number of standard time zones. Roughly speaking, there are 24 time zones spaced at intervals of 15° in longitude. (Practically, due to geographic and political factors, the boundaries of time zones are more circuitous.) The areas in the eighth time zone of Eastern Hemisphere should in principle use standard time UTC+8. Therefore SST is UTC(SG) + 8. But, there is no official international register of national time zones. Any country is free to choose and vary its time zone(s) at it pleases.

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How many countries have standard time? How many in Asia?

About 50 time metrology laboratories from 30 countries around the world keep about 50 local time scales UTC(k) which approximate UTC.
In Asia, the other following countries have their own national time standard.
Australia, China, Chinese Taibei, India, Japan, Korea, New Zealand, Malaysia, Thailand, Uruguay.

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