I'm not asking about the length of daylight for the winter solstice. I'm asking about whole days that are shorter than 24 hours. For example, anywhere that observes Daylight Saving Time has one day each year that is 23 hours long. Any location that decides to change time zones can also experience a longer or shorter day, that day. Given all such factors, where and when was the shortest day? You can ignore days that were skipped entirely.

PS: I'd love to know the longest day, too.

EDIT: Imagine a person with a desktop calendar, one page per day. Every "day" he flips one page of his calendar, or more pages at once if he is changing calendar systems. I want to know how close together two such separate flipping events would have occurred.

  • This is a surprisingly difficult question to answer. In fact, it turns out that the definition of a day isn't even a simple matter. – T.E.D. Jun 25 '15 at 19:23
  • @T.E.D. well, I'll take answers for any plausible definition of a day. I'm mostly looking for "time elapsed between changes to the current date in the local calendar" – Sparr Jun 25 '15 at 19:26
  • Well, the trouble I ran into is that there are lots of plausible definitions. – T.E.D. Jun 25 '15 at 19:34
  • @MarkC.Wallace see my CW answer regarding China – Sparr Jun 25 '15 at 19:59
  • I've edited in your unstated requirement. Feel free to revert the edit if you don't like it. – Spencer May 17 '18 at 22:35

The day that western China switched from local time to the now-standard UTC+8 (the same as eastern China, four normal time zones away), some cities/provinces there should have experienced a 20 hour day. I am making this answer CW so that someone more knowledgeable can fill in the historical details.

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    Westernmost major city in China, Kashgar, is located at 76°E, which means it's natural solar time is about UTC+5. If they switched directly from UTC+5 to UTC+8 (I don't know whether that ever was the case) they'd have experienced a 21 hour day, 20 hour seems impossible to me. – Bregalad May 16 '18 at 17:39
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    Another good candidate is Crimea, which lived a 22 hour day when it switched directly from Ukraine's winter time (UTC+2) to Russia's back then permanent sommer time (UTC+4) experiencing a 22 hour day. Since then Russia reverted to permanent winter time UTC+3. – Bregalad May 16 '18 at 17:45
  • According to wikipedia, western China had only UTC+5h30 time zone before the global switch to UTC+8, and then regularly switched back and forth between +6 and +8 (+6 being used unofficially even today). So it should be investigated whether this 21.5 hour day ever existed when switching from UTC+5h30 to UTC+8. – Bregalad May 18 '18 at 12:25

I nominate the Alaska Purchase as causing the shortest calendar day. Russia still used the Julian calendar, so when the transfer occurred, so did the calendars, with October 6, 1867 suddenly becoming October 18, 1867.

The transfer appparently occurred at 3:30 pm, meaning October 18, 1867 technically lasted only 8 and a half hours (using a very strict definition for "technically").

  • Was there about 15.5 hours of October 6 immediately preceding it? – Sparr Jun 17 '18 at 5:14
  • @Sparr I would imagine. I've been unable to find anything about how the average Alaskan dealt with this calendar anomaly though. – DPenner1 Jun 17 '18 at 5:17
  • I'll note that after a second round of searching, I've still been unable to locate a primary document referencing the calendar changeover - take this answer with a grain of salt. – DPenner1 Dec 27 '18 at 21:27
  • This answer is interesting because I did not originally consider the possibility of a single ~24 hour period being split into two whole short days. – Sparr Dec 28 '18 at 1:53

Some places have seen a whole day pass in an instant. December 30th 2011 had no duration at all in Samoa and Tokelau:

Samoans who had gathered around the main clock tower in the capital, Apia, cheered and clapped as the clock struck midnight on Thursday to the wail of sirens and burst of fireworks and time jumped forward 24 hours to Saturday. Drivers circled the clock tower blaring their horns, and prayers were held across the country. The change effectively erases Friday 30 December 2011 from its calendar.

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    But this would put the later Gregorian Calendar chagers in the lead. Bulgaria, Greece, Russia, Estonia and Turkey all lost 13 days in the Early. 20th Century. – Spencer May 17 '18 at 22:31

I posit that, wherever the change occurred between the Julian calendar (O.S.) and the Gregorian calendar (N.S.), that constituted the shortest day -- indeed, a group of them -- since the span of days skipped therefore became non-existent. Those days could thus be interpreted as zero hours long.

  • Interesting edge-case answer. However, I sorta expect the answer I'm looking for to be in the vicinity of 20 hours. – Sparr Jun 25 '15 at 19:54

If you were on an 18th Century British warship, the day started at noon rather than midnight (12 hours behind). If you arrived in port in the afternoon and then stayed ashore overnight, your day would have been 12 hours long.

Of course, if you're allowed to travel and cross the international date line, then the day can be as long or short as you like.

  • Interesting. I'm mostly interested in stationary locations, though. – Sparr Jun 25 '15 at 20:20

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