The question was, "LeapSeconds can cause a day to be more or less than 24*60*60 seconds long. What else can?"

Please put your answers here or so:

	* Shift from daylight savings time to standard time -- KielHodges

That was the answer I had in mind when I asked the question. Midnight to midnight, the day we change to daylight savings time is twenty-three hours long; the day we change back is twenty-five hours long. (This caused a serious problem in logging software on a project I worked on.) -- PaulChisholm

I HadThisPattern recently as well (see http://radio.weblogs.com/0122027/2003/10/17.html#a91 ) It's funny, every time I see something like secondsInDay = 24*60*60, I always used think to myself "what about leap seconds?" but rarely about the daylight savings time shift. (This is an advantage of working with a library that has a robust representation of time, to increment a date by one day, do something like date.addDay(1) or date.add(1,"DAY") or whatever). -- RodWaldhoff

These other answers are like the old puzzle/joke about using a barometer to measure the height of a building:

	* A visit from the in-laws
	* Travelling across a timeline. This may seem like cheating, but the programmers of the control systems on a 767 probably wouldn't think so. -- JeromeKaraganis
	* Being on a different planet.
	* Travelling VERY fast or sitting next to a black hole. ''[Nope. All you can say is that two clocks can be made to disagree - that doesn't change the number of seconds they count in one of their days.]'' Not really a fair criticism, you can say that about nearly '''all''' of these answers, including the "official" one!
	* Y2K. If you're not lucky, December 31, 1999 may be -100 years long.
	* Living before God let there be light. Read about the Scopes monkey trial for an explanation.
	* redefining CLK_TCK/CLOCKS_PER_SECOND ''[Nope, still 24*60*60 seconds/day]''
	* floating point roundoff?
	* According to a news report, El Nino winds had a measurable effect on the Earth's rotation. Something like (?) 1/4 milisecond.
	* If time should ever turn out to be quantized, and 24*60*60 seconds is not fully divisable by a time quantum (may not be possible, depending on the exact definition of a second). :-)
	*What's a day? A sidereal day is about 4 minutes different than a solar day.
	* Loading a file on a Commodore 64 using the standard load command.
	* Black hole the sun
	* Shift to a metric timebase. Lets shift to 10 days per (metric) week, while we're at it.
	* Redefine the timebase so that c (the speed of light in a vacuum) is some convenient multiple of 10 meters per metric second.
	* First convince the majority of people that anything is possible. Second, convince them via magic or science or religion that the day is longer. That's it. Reality is not so real!
	* A sudden failure of the Earth to continue rotating?
	* Meteor impact, or even a well-placed close call.
	* Shooting a million sufficiently large projectiles, from a million sufficiently large cannons in either an easterly or westerly direction (in the same day) in such a way that the projectiles achieve escape velocity.
	* GlobalWarming, GlacialMelting, SeaLevelRise -- resulting in a change in the dissipation of tidal energy both from the Moon's orbit and Earth's orbit around the sun - Internal''''''Waves may change their dissipation rates, increasing or decreasing in - as yet - unpredictable ways. -- ChrisGarrod