GMT is the name given to MEAN SOLAR TIME at the Greenwich meridian; it is the popular name for civil time kept in the UK. The need for a standard time across the country came with the development of the railways, from 1825 onwards. For example, passengers travelling from Bristol to London would find a ten-minute difference between the time kept in the two cities because local time, measured according to the position of the Sun in the sky, varies with longitude. Eventually the railways adopted Greenwich time, which became known as ‘railway time’, as their standard and in 1880 it became the legal time for the whole country. In 1928 the INTERNATIONAL ASTRONOMICAL UNION (IAU) recommended that Greenwich Mean Time should become the Standard timescale for scientific purposes and be known as UNIVERSAL TIME (UT). Today, Greenwich Mean Time is still the standard against which the system of TIME ZONES around the globe is measured, each one being an integral number of hours ahead of or behind it.