Coordinated Universal Time (UTC – from the French Temps Universel Coordonné) is an international timescale based on the time told by atomic clocks. Atomic clocks are accurate to within a second in several million years. They are so accurate that International Atomic Time, the time relayed by these devices, is even more accurate than the spin of the Earth.
The Earth’s rotation is affected by the gravity of the moon and can therefore slow or speed up. For this reason, International Atomic Time (TAI from the French Temps Atomique International) has to have ‘Leap seconds’ added to keep it in line with the original timescale GMT (Greenwich meantime) also referred to as UT1, which is based on solar time.
This new timescale known as UTC is now used all over the world allowing computer networks and communications to be conducted at opposite sides of the globe.
UTC is governed not by an individual country or administration but a collaboration of atomic clocks all over the world which ensures political neutrality and also added accuracy.
UTC is transmitted in numerous ways across the globe and is utilised by computer networks, airlines and satellites to ensure accurate synchronisation no matter what the location on the Earth.
In the USA NIST (National Institute of Standards and Technology) broadcast UTC from their atomic clock in Fort Collins, Colorado. The National Physics Laboratories of the UK and Germany have similar systems in Europe.
The internet is also another source of UTC time. Over a thousand time servers across the web can be used to receive a UTC time source, although many are not precise enough for most networking needs.
Another, secure and more accurate method of receiving UTC is to use the signals transmitted by the USA’s Global Positioning System. The satellites of the GPS network all contain atomic clocks that are used to enable positioning. These clocks transmit the time which can be received using a GPS receiver.
Many dedicated time servers are available that can receive a UTC time source from either the GPS network or the National physics Laboratory’s transmissions (all of which are broadcast at 60 kHz longwave).
Most time servers use NTP (Network Time Protocol) to distribute and synchronise computer networks to UTC time.