It’s that day when everyone in the US pays attention to time zones, because we all lost an hour of sleep tonight. And at least in my case, I’ll be a bit bitter tomorrow morning, when the sun rises at 7:56 in Atlanta – a city that really should be on Central Time, but is presumably Eastern because, well, look at a map, Georgia is on the East Coast. (For a cheap thrill, drive to Alabama in less than an hour – as you can do on I-20. Then set your clock back and have arrived before you left.)
Time zones are basically a clustering problem with some extra restrictions. You want to set times so that:
- Almost everybody’s time differs by a whole number of hours from UTC;
- Clock times are not too far from solar time;
- The time where you are is the same as the time in nearby places you communicate with.
- Time zone boundaries align with geographical boundaries
The second of these criteria keeps time zones narrow; the third keeps them wide. The Basement Geographer has some examples where keeping the time zones wide – as in countries like Brazil, Russia, India, or China – means time zone boundaries with neighboring countries that aren’t the standard one-hour change upon moving east or west. And Alison Schrager at Quartz has suggested that the US should have two time zones, one hour apart. (These would be UTC-5 in the east and UTC-6 in the west.). All of Western Europe being on UTC+1 is another example – although from what I understand there’s some World War II history tied up in here. France, for example, was on UTC before the war – although the law called it Paris mean time, retarded by nine minutes and twenty-one seconds. Anything to avoid letting the British win.
God plays dice 