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Two countries in the same time zone, will always have the same time. #16

Open aquaticfig opened 7 years ago

aquaticfig commented 7 years ago

Daylight savings sometimes begins/ends at different dates even for countries in the same time zone. This sounds innocent! It isn't. I used to coordinate cross-border activities between Israel and Lebanon. Some of these activities were controlled demolitions of bombs or mines. Back then, we switched about a whole month earlier than in Lebanon because of Yom Kippur (for ridiculously illogical reasons you might find entertaining if you google them. I think they've changed it since then, but who can keep track - I'm out of the army now). Anyway, for that entire month, people would forget about the time difference ALL THE TIME. Soldiers on patrol would almost get hurt because they were told to avoid a certain stretch of border during one time period, when in fact the mine was being defused/exploded an hour before. Or an hour later. (It was really confusing, okay??) And then, because personnel got rotated every 1-2 years, you'd have fuckups every. single. year.

aquaticfig commented 7 years ago

Oh, and another annoying way this manifests: "Two locations on the globe will always have the same time difference between them" - also false for the same reason.

ewjoachim commented 7 years ago

But are Israël and Lebanon using the same time zones ? As far as I can tell, there is an Asia/Jerusalem time zone and an Asia/Beirut...?

aquaticfig commented 7 years ago

We're both UTC+02:00, but each country can make different decisions regarding things like Daylight Savings. That's why it's defined as two different clocks when setting a time zone on a computer, for instance.

https://en.wikipedia.org/wiki/Israel_Standard_Time

(ETA: Whoops, turns out that I did not understand what the 'comment and close' button meant!)

ewjoachim commented 7 years ago

Well, that all boils down to how you define "time zone". The "usual" definition with 24 zones defined roughly by meridians, or the technical definition with tz database defining currently 561 zones, defined by : "any national region where local clocks have all agreed since 1970.".

By technical definition, 2 places in the same timezone will always be on the same time, because that's what defines them as being in the same timezone. With the "24 time zones" definition, of course, that's not true, and there are numerous examples. But... This definition is quite lacking precision anyway.