Time zones

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.


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