time (DST, or summer time), whereby clocks are advanced one hour during the lighter summer months so that evenings have more apparent daylight and mornings have less. DST was first implemented during the First World War, mainly to more closely match the hours that people are awake, thereby lowering the need for artificial light and conserving fuel. Many other countries have used it since then, and many still do, including most of Europe and North America.

Greenwich Mean Time (GMT)

Greenwich Mean Time (GMT) was the earliest internationally accepted time standard. It was established at the International Meridian Conference in 1884, when it was decided to place the Prime Meridian (0° longitude) at Greenwich, England, although Greenwich was already widely used as a standard since the establishment there of theRoyal Observatory in 1675. It is a telescope-based standard, with noon GMT defined as the average (mean) time at which the Sun crosses the Prime Meridian and reaches its highest point in the sky there. Other time zones across the world, as used in Standard Time (see above), are defined in terms of offsets from GMT, so that all clocks within each time zone are set to the same time as the others. GMT was superseded as the main international standard by Universal Time (see above) in 1928, although UT is still often referred to informally as GMT.

GPS Time

GPS Time is the time standard used by the Global Positioning System (GPS), the space-based satellite navigation system, first developed in 1973 and made fully operational in in 1995, that