On Tue, Sep 22, 2015 at 10:27 PM, Chris Angelico <[email protected]> wrote:
> [ Alexander Belopolsky] but I cannot tell you "mean" of what it is or > whether BBC's > > fifth beep comes on a UTC or GMT second. > > Yes, it's because GMT is based on the average solar noon. If you have > an actual sundial, you can observe actual solar noon, but to convert > that to civil time, you need a table of translations that takes > seasonal variation into account. In theory, Greenwich Time would show > noon when the sun is directly overhead, but that would mean that > successive days vary in length; Greenwich Mean Time averages it all > out so you get a consistent 86400-second day. > > UTC is defined by the coordination of a bunch of clocks around the > world. There are a few different forms, most of which never go more > than one second away from each other. GMT is usually defined as being > equal to one or other of them, but which one is not entirely > standardized, so if you need subsecond accuracy, don't use GMT at all. > For scheduling events, though, GMT == UTC == TIA == Unix time. > Thanks for the lecture, but I still don't know what BBC broadcasts. :-)
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