What does GA mean in TIME ZONES

UTC (Coordinated Universal Time) is the primary global standard used to regulate time and measure intervals of time, such as days, hours, minutes, and seconds. It is an atomic-based time scale that is globally accepted and monitored by the International Earth Rotation and Reference Systems Service (IERS).

Greenwich Atomic (also known as GMT or Greenwich Mean Time) was the name used in the United Kingdom for Coordinated Universal Time (UTC) prior to 1964. UTC replaced Greenwich Atomic when it became the international standard for specifying time.

The main difference between UTC and Greenwich Atomic was that UTC was based on an atomic clock, while Greenwich Atomic relied on astronomical observations. As a result, UTC is more accurate than Greenwich Atomic as it has much less fluctuation when taking into account leap years and other forms of variation due to the position of the earth relative to the sun.

The United Kingdom switched from using Greenwich Atomic to using UTC because it's more accurate than relying on astronomically measured positions of the Earth relative to the Sun. The UK wanted a single, internationally recognized time zone in order for them to keep track of their day-to-day schedules with greater accuracy than before.

One advantage of using UTC rather than GMT (or any other alternating means of measuring time) is that it's based on an atomic clock rather than relying on solar observations. This makes it much more reliable when dealing with issues such as variations due to leap years or changes caused by nutation or precession which can cause fluctuations in a solar-based system but have no effect on an atomic clock based one. Additionally, since both sunrise/sunset times and conventional clock times vary depending on longitude, utilizing an atomic-based system ensures everyone around the world can use exactly same definition of what constitutes a 'minute' or 'hour.'

People started using Coordinated Universal Time instead of GMT in Britain in 1964. This transition occurred after countries around the world adopted “Universal Time” as their official benchmark for measuring time zones instead of individual countries relying on their own local systems such as GMT for specific timescale measurements.

Yes - although both are based off an atomic clock providing universal timing standards, TAI provides an absolute measurement free from any form of relativity that would slow down or speed up its measurement over traditional timekeeping methods which take into account relativity factors such as leap seconds or spin rate adjustments due to nutation or precession movement which can affect solar-based systems like GMT/UT1 but not TAI/UTC which rely solely on precise timing measurements from precise electronic clocks synced worldwide at regular intervals via GPS signals..