Where is the UST time zone?

Answer 1

Short answer: Greenwich, London, UK, kind of, assuming daylight savings time isn't in effect.

Longer answer:

UST Time is an unofficial synonym for UTC, Coordinated Universal Time. UTC is based on TAI, which is the average of hundreds of atomic clocks around the world. To get UTC they take TAI, and adjust it (using leap seconds) to keep it less than a second off of UT1.

UT1 is the mean solar time above the Royal Observatory, Greenwich, which is located in the greater London metropolitan area in the United Kingdom. So, UST/UTC is a virtual time zone that's located no place, but for all intents and purposes is located in the Royal Observatory, since that's the time it most closely tracks.

Since it's coordinated with a solar time, rather than local time, it's based on the movement of the earth and the sun, and is not affected by daylight savings time or any other political decisions that happen around time. This means that while UST/UTC is based on the solar time at the Greenwich Observatory, it might be an hour off of the clock at the pub closest to the Observatory, and your local time might change its relationship to UTC, often by an hour back and forth each year.

GMT (Greenwich Mean Time) is the old name for UTC.