Ask Slashdot: How Many Time Standards Are There?

jjoelc writes "Being one of those 'suffering' through the time change last night, the optimist in me reminded me that it could be much worse. That's when I started wondering how many different time/date standards there really are. Wikipedia is a good starting point, but is sorely lacking in the various formats used by e.g. Unix, Windows, TRS-80, etc. And that is without even getting into the various calendars that have been in and out of use throughout the ages. So how about it? How many different time/date 'standards' can we come up with? I'm betting there are more than a few horror stories of having to translate between them..."

Comments

Time Standards vs. Time Formats, and Y10K problem

[girlinatrainingbra]

IMHO, Time Standards would be "standards/standardizations for time keeping", such as say when the railroads crossed the US and decided that local high-noon was not so useful when you translate yourself geographically so swiftly, and thus "time zones" in the US were set up. Some countries (India, and China, maybe others i don't know of...) keep a signle time zone for the entirety of their contiguous expanse for "standardization".
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Time Formats, again IMHO, would be the "standard" (ha, I heard it [that word] both ways!) used for displaying, communicating, or storing "time data values" on paper, verbally, or in a computerized (or book-keeping) record. One example: "yYYYY-MM-DD-HH-mm-ss.{fractional value of second}" [note I added an extra "y" digit to allow for the Y-10K problem!!!). Floppy disks and TRS-DOS and Apple DOS and MS-DOS and CPM and UNIX and so many others use different formats for this. They also use different "loci" for the "origin point" of time (the "epoch", e.g. time elapsed since point $x$ in time. Gregorian year 1904 for old macs, 1970 for the unix epoch, etc.

Critical Dates

[Sebastopol]

on a side note, i love this website:

http://www.merlyn.demon.co.uk/critdate.htm

it is a huge list of important dates relevant to computer programs, algorithms, and O/Ses.

Re:Total

[ericloewe]

http://xkcd.com/1179/

ISO 8601

But, since you mention the overabundance of standards...

http://xkcd.com/927/

Re:Time Standards vs. Time Formats, and Y10K probl

[OneAhead]

Dude, how on earth can you get it all so badly wrong? Is this a subtle postmodernist troll or something? Sorry if it isn't, starting a discussion on a scientific subject with "IMHO" sets off my bullshit alarm.

Historically, a day was defined as 1 earth rotation. An hour was 1/24th of a day, a minute as 1/60th of an hour, and a second as 1/60th of a minute. Hardly very arbitrary, is it? Problem is, turns out that there are constant fluctuations and drift on the length of a celestial day (and year). This is very impractical because there are no known clock mechanisms (bar the solar system itself) that can catch these fluctuations, so humanity needed a more solid definition of time for entirely irrelevant tasks such as performing precise scientific measurements and keeping GPS sattellites in sync. Common off-the-shelf clock mechanisms couldn't be used for this purpose because they also fluctuate too much. Instead, we redefined the lenght of a second based on an immutable physical property: the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Cesium was "arbitrarily" chosen because of atomic clock engineering and accuracy considerations, the hyperfine transition was "arbitrarily" chosen because it is not too easy to skew, directly relates to a physical constant and can be measured in a reasonably convenient way, and the number 9,192,631,770 was "arbitrarily" chosen to make the SI second as close as possible to the then-best estimate of the average duration of the celestial second (1/86400 of a day). Then we redefined the SI minute, hour, day,... based on that physically immutable(*) second. Problem is, that didn't stop the earth rotation and solar system from fluctuating. And that's why we have leap seconds now and then; to keep our non-arbitrary SI-based time in sync with the arbitrary vagaries(+) of the solar system.

(*) Well, pretty immutable for the practical applications you're going to care about. There's always room for improvement.
(+) To be precise, orbital mechanics are well-understood so in that sense they're not random.(#) Problem is, it's a chaotic system, so no matter how precise we measure all the boundary conditions, a simulation of the solar system will over time deviate more and more from reality. That's why leap seconds are based om measurements.
(#) If you look even deeper into the subject, there are solar winds and weather-dependent tidal effects contaminating the whole shebang with fluctuations we can't even predict a few weeks in advance because they're complex. So yeah, arbitrary.