On Apr 1, 2015, at 5:15 PM, Keith F. Lynch <kfl@KeithLynch.net> wrote:
Dan Asimov <asimov@msri.org> wrote:
It's still March 31 in my time zone.
It was April 1st where I was, and it was April 1st UTC. Thanks to how the International Date Line meanders, there's no instant when it's April 1st everywhere. You're in the Pacific zone?
Yes, I am. And your mention of the International Date Line reminds me of a (genuine) little math puzzle, and a related geographical enigma: ----- 1. Suppose Earth is a perfect sphere and that each time zone is a perfect spherical lune of angle 2π/24 that takes 1 hour to traverse an hour of time. Set a stopwatch to begin when it is first mm/dd/yyyy anywhere on Earth, and stop the watch when it is no longer mm/dd/yyyy (where mm/dd/yyyy is an arbitrary day of 24 hours' length). QUESTION: How long did the stopwatch run for? (Mental math only.) ----- 2. Same question, but with time zones as they actually are. (Any references and writing implements allowed.) ----- Note: I don't know the answer to 2. --Dan