What is the Correct Time? The Development of Time Scales from GMT to UTC and NTP Servers

By: Richard N Williams

Askingsomebody the time may be one of today’s most common questions but have you everwondered where the time on our watches comes from?

Accurateclocks have only been around since the mid 17th century, before then,time was completely subjective. People would use the celestial bodies as a timereference such as noon (when the sun was highest) and midnight (when the moonis at its highest) and also dawn and dusk. Often lengths of time were referredto in comparison such as the time it would take a man to walk a mile.

Standardtimescales did not exist until the 1840’s when it became necessary during theheight of the railway’s popularity when a railway standard time for allEngland, Wales and Scotland replaced all the local timescales.

A few yearslater the Royal Observatory in Greenwich developed its own time scale. This wasbased on the sun and moon, with 12 o’clock (noon) being when the sun was overthe Greenwich Meridian, they began transmitting this timescale using thetelegraph and by 1855 most of Britain used GMT (Greenwich Mean Time) and it soonbecame a recognized time reference throughout the world.

However, itbecame apparent with the invention of atomic clocks that basing a timereference on the movement of the Earth was not accurate enough. In 1967 thesecond was defined by the oscillations of the caesium -133 atom (as used inatomic clocks) and provided the most accurate reference for time yet but attemptsto couple GMT with this new definition proved unsatisfactory when it wasdiscovered that the Earth slows (and speeds up) on its axis.

This variationsin the rotation of the Earth meant a new timescale UTC, (Coordinated UniversalTime) which made adjustments for this slowing adding (or subtracting) a secondwhen ever necessary (failure to do so would mean eventually day would becomenight as time would slipPsychology Articles, albeit in many millennia). This addition is known asa Leap Second.

UTC hasbecome vital in allowing the global community to communicate with each other.UTC allows the world to synchronise to one time scale regardless of the timezone (UTC handles timezones with a + or minus such as UTC +5 or UTC -2)

UTC enablescomputers to synchronise together all over the world using NTP (Network TimeProtocol). Without NTP it would be impossible to conduct time sensitivetransactions such as buying an airline ticket or bidding on Ebay.

Most NTPtime servers receive UTC time atomic clocks from either a broadcasted signalfrom a large physics laboratory or via the GPS network.

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