The distinction between different kinds of time is really pretty key to having a clear understanding. Civil time is different from atomic time and different fr

The distinction between different kinds of time is really pretty key to having a clear understanding. Civil time is different from atomic time and different from sidereal time or solar time. Civil time is how people, businesses, and governments organize and plan their activities. Atomic time is monotonic, physical, and "more objective" / less dependent on legislatures :) Sidereal time is about the orientation of Earth relative to stars. It's really important if you're an astronomer. UTC is a civil time standard based closely on TAI, an atomic time standard, except it gets corrected to be within 1 second of UT1, a sidereal time standard. It is basically _the_ civil time standard and it is a little compromise to make a civil time that advances like atomic time but also does not desync from sidereal time. Different administrative regions use offsets from UTC to determine their local civil time. If you're writing an application where people plan future activities and you really want to "get things right / not surprise users", you probably need to store times in the appropriate civil time standard, make it apparent _which_ civil time standard is canonical per activity if people are being coordinated across administrative regions that do not synchronize their standards, and ensure that your application can find out about planned changes to civil time in any of the administrative regions of interest.