The 24 hours I lost when crossing the international date line

Mr. Mat Man: As I prepared to cross the international date line, an interesting question presented itself. What happens to the 24 hours I lost when I crossed it? The easy answer is that I would gain the time back upon crossing the other way on my return. But I'm currently aboard the aircraft carrier USS Nimitz heading west on an around-the-world cruise. So when I get home in March, will I still be one day ahead of my wife? Does this mean that I will have been married one day more than her? — LT Randall Ingels, USN, at sea

Well, that’s why they call it the international date line. On that extra day, you get to grab an international date and go out and raise all kinds of hell, because in the real world, the day never happened. Well, maybe not....

Actually, it works like this. The big pie that is Earth is cut into 24 slices, each the width of 15 degrees longitude. Time zones. The meridian through Greenwich, England, is the zero degree point in the system. As you chug west, you set your watch back one hour as you enter each new pie wedge. As you steam east, you set it one hour ahead. Circumnavigate the pie, and it all evens out. But for bookkeeping purposes only, not for astronomical time-space reasons, at the 180 degree point, the date line, we need to relabel the new day. Calendar and clock time, after all, are just arbitrary but generally agreed upon names.

When it’s a minute after noon Tuesday, counting pie wedges going east, it’s a minute after midnight at the international date line, one minute into Wednesday because you’ve “gained” 12 hours. Going west, at that same point, your watch would also read 12:01 a.m„ but you’re only one minute into Tuesday, because you’ve “lost” 12 hours. The time-zone design committee realized that for social-political-economic reasons, we’d have to relabel our day at the 180 degree point in the pie. One of the reasons the date line is in mid-Pacific is to minimize the confusion. If it ran through Chicago or Munich or Moscow, all of commerce would grind to a halt.