4 ms·

Earth already has this problem. Years aren't consistent both because the number of rotations don't evenly go into a single revolution, but also because Earth's

Earth already has this problem. Years aren't consistent both because the number of rotations don't evenly go into a single revolution, but also because Earth's rotation time is variable. For instance, above normal fresh water accumulation on land will measurably change the length of a day. Generally, there are two solutions. One is to track absolute time by increasing the clock as necessary to realign the day to the year. There are Earth days with where the last minute of the day is 61 seconds long. Daylight Saving Time makes days with 23 hours or 25 hours. And, of course, leap years add a day. Unfortunately, a lot of software/hardware is built by people with misconceptions about time, like a minute can have only 60 seconds or a day can have only 24 hours. So, the second solution is to update the system periodically. Computers often poll internet time to update the clock and will jump to the new time. Alternatively, some systems skew the system clock with additional milliseconds per second until it catches up with the time change. As long as the values are valid typical ranges, most software doesn't care about sudden changes.

anticristi 5y ago
Very well summerized. For those who care about the longer version: https://en.m.wikipedia.org/wiki/International_Atomic_Time https://en.m.wikipedia.org/wiki/International_Atomic_Time https://en.m.wikipedia.org/wiki/Universal_Time https://en.m.wikipedia.org/wiki/Universal_Time https://en.m.wikipedia.org/wiki/Coordinated_Universal_Time https://en.m.wikipedia.org/wiki/Coordinated_Universal_Time
- benpbenp 5y ago
  > Very well summerized. Actually, in Sumer, they used an intercalary month every three years or so, much like the leap year in the Gregorian Calendar. https://en.wikipedia.org/wiki/Sumer https://en.wikipedia.org/wiki/Sumer
dotancohen 5y ago
> Years aren't consistent both because the number of rotations > don't evenly go into a single revolution, but also because > Earth's rotation time is variable. Lots of civilizations have found novel solutions to the fact that the number of days in a year is not an integer. Adding an occasional leap month (Hebrew calendar) or leap day (Gregorian calendar), or just letting the calendar get out of sync with the seasons (Islamic calendar). However, it should be noted that although the Earth's rotation time is measurably variable, such measurements require precision instruments that have only been available for a bit over a century. Human senses could not notice such small changes over the course of a lifetime or even over the lifespan of an empire.
- dfsegoat 5y ago
  > Human senses could not notice such small changes over the course of a lifetime or even over the lifespan of an empire. I don't disagree in this case. But I am continually amazed at how resourceful and technical past civilizations could be. For instance early polynesian navigators ("wayfinders") could look at patterns in wave refraction across the ocean surface, to locate islands over the horizon [1]. They also memorized the setting and rising positions of hundreds of stars. [1] Unfortunately, much of this knowledge was lost, as the polynesians did not have a written system of language. 1 - https://manoa.hawaii.edu/exploringourfluidearth/physical/navigation-and-transportation/wayfinding-and-navigation https://manoa.hawaii.edu/exploringourfluidearth/physical/nav...
  - wahern 5y ago
    > Unfortunately, much of this knowledge was lost, as the polynesians did not have a written system of language. Having a writing system might have been sufficient to prevent the loss, but not necessary. I'd argue the immediate cause was the disappearance of folk songs and similar rituals that encoded this knowledge in the culture. > In Oceania’s oral culture, narrative was the primary tool to memorize and transmit complex accounts of interconnected voyaging routes through the sea of islands. These accounts would have been replete with their respective star (and sun) courses, with bearings, instructions for seasons for travel, the expected quality of swell, winds, sea marks and other indispensable information for reckoning and island finding. In other words, Oceanic geography was, like Oceanic history, genealogy and all other matters of education, a narrative art, taught and memorized at specialized marae primarily through the recitation of chants. https://www.tandfonline.com/doi/full/10.1080/00223344.2018.1512369 https://www.tandfonline.com/doi/full/10.1080/00223344.2018.1... (Lars Eckstein and Anja Schwarz, The Making of Tupaia’s Map: A Story of the Extent and Mastery of Polynesian Navigation, Competing Systems of Wayfinding on James Cook’s Endeavour, and the Invention of an Ingenious Cartographic System) Unfortunately it seems that these particular oral traditions lost their fidelity before the age of audio recording. The introduction of writing systems has preserved much knowledge, but it has also destroyed much knowledge by supplanting other modes of preservation. I'm not even sure which is greater. Most of the utility in the adoption of writing systems is prospective, I think. Interestingly, modernity may be its own worst enemy in this regard. A friend recently pointed me to this experiment that pitted Memory Palaces against an Australian Aboriginal memorization technique[1] by assigning incoming medical students to three different groups: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251710 https://journals.plos.org/plosone/article?id=10.1371/journal... The authors' conclusion was that the aboriginal technique offered substantially superior recall, but they refrained from detailing the technique out of fear of cultural insensitivity! sigh Maybe it would have been insensitive, and maybe they did the right thing, but the irony is astounding. [1] Apropos the navigation theme, the technique seems to be one way Aborigines teach their star charts. In fact, the technique itself seems to encode some cultural knowledge, which is presumably why even providing the details might seem culturally invasive--because such knowledge isn't intended for outsiders, except unless taught by a member.
swiley 5y ago
Yeah, a lot of people don't realize you can't compare intervals of UTC seconds without an almanac generated by a random natural process.
vikiomega9 5y ago
> for instance, above normal fresh water accumulation on land will measurably change the length of a day Is there a name for this that I can google for?
- echelon 5y ago
  I was curious: https://en.wikipedia.org/wiki/Day_length_fluctuations https://en.wikipedia.org/wiki/Day_length_fluctuations
- HPsquared 5y ago
  The general physics concept is moment of inertia. If water is moved uphill, this redistributes some of the Earth's mass further away from the axis of rotation, which increases its moment of inertia. Since the total angular momentum of the Earth is not changed by doing this, the result is a reduction of the angular velocity, in other words lengthening the day. NASA calculated, for instance, that filling the Three Gorges Dam reservoir would lengthen the day by 0.06 microseconds.
  - swader999 5y ago
    I wondered why the days felt longer. Thanks.
dmoy 5y ago
The time smear (not skew, really) method works very, very well, for almost everything Here's as pretty good summary: https://developers.google.com/time/smear https://developers.google.com/time/smear

anticristi 5y ago

Very well summerized. For those who care about the longer version: https://en.m.wikipedia.org/wiki/International_Atomic_Time https://en.m.wikipedia.org/wiki/International_Atomic_Time https://en.m.wikipedia.org/wiki/Universal_Time https://en.m.wikipedia.org/wiki/Universal_Time https://en.m.wikipedia.org/wiki/Coordinated_Universal_Time https://en.m.wikipedia.org/wiki/Coordinated_Universal_Time

benpbenp 5y ago
> Very well summerized. Actually, in Sumer, they used an intercalary month every three years or so, much like the leap year in the Gregorian Calendar. https://en.wikipedia.org/wiki/Sumer https://en.wikipedia.org/wiki/Sumer

dotancohen 5y ago

> Years aren't consistent both because the number of rotations > don't evenly go into a single revolution, but also because > Earth's rotation time is variable. Lots of civilizations have found novel solutions to the fact that the number of days in a year is not an integer. Adding an occasional leap month (Hebrew calendar) or leap day (Gregorian calendar), or just letting the calendar get out of sync with the seasons (Islamic calendar). However, it should be noted that although the Earth's rotation time is measurably variable, such measurements require precision instruments that have only been available for a bit over a century. Human senses could not notice such small changes over the course of a lifetime or even over the lifespan of an empire.

dfsegoat 5y ago
> Human senses could not notice such small changes over the course of a lifetime or even over the lifespan of an empire. I don't disagree in this case. But I am continually amazed at how resourceful and technical past civilizations could be. For instance early polynesian navigators ("wayfinders") could look at patterns in wave refraction across the ocean surface, to locate islands over the horizon [1]. They also memorized the setting and rising positions of hundreds of stars. [1] Unfortunately, much of this knowledge was lost, as the polynesians did not have a written system of language. 1 - https://manoa.hawaii.edu/exploringourfluidearth/physical/navigation-and-transportation/wayfinding-and-navigation https://manoa.hawaii.edu/exploringourfluidearth/physical/nav...
- wahern 5y ago
  > Unfortunately, much of this knowledge was lost, as the polynesians did not have a written system of language. Having a writing system might have been sufficient to prevent the loss, but not necessary. I'd argue the immediate cause was the disappearance of folk songs and similar rituals that encoded this knowledge in the culture. > In Oceania’s oral culture, narrative was the primary tool to memorize and transmit complex accounts of interconnected voyaging routes through the sea of islands. These accounts would have been replete with their respective star (and sun) courses, with bearings, instructions for seasons for travel, the expected quality of swell, winds, sea marks and other indispensable information for reckoning and island finding. In other words, Oceanic geography was, like Oceanic history, genealogy and all other matters of education, a narrative art, taught and memorized at specialized marae primarily through the recitation of chants. https://www.tandfonline.com/doi/full/10.1080/00223344.2018.1512369 https://www.tandfonline.com/doi/full/10.1080/00223344.2018.1... (Lars Eckstein and Anja Schwarz, The Making of Tupaia’s Map: A Story of the Extent and Mastery of Polynesian Navigation, Competing Systems of Wayfinding on James Cook’s Endeavour, and the Invention of an Ingenious Cartographic System) Unfortunately it seems that these particular oral traditions lost their fidelity before the age of audio recording. The introduction of writing systems has preserved much knowledge, but it has also destroyed much knowledge by supplanting other modes of preservation. I'm not even sure which is greater. Most of the utility in the adoption of writing systems is prospective, I think. Interestingly, modernity may be its own worst enemy in this regard. A friend recently pointed me to this experiment that pitted Memory Palaces against an Australian Aboriginal memorization technique[1] by assigning incoming medical students to three different groups: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251710 https://journals.plos.org/plosone/article?id=10.1371/journal... The authors' conclusion was that the aboriginal technique offered substantially superior recall, but they refrained from detailing the technique out of fear of cultural insensitivity! sigh Maybe it would have been insensitive, and maybe they did the right thing, but the irony is astounding. [1] Apropos the navigation theme, the technique seems to be one way Aborigines teach their star charts. In fact, the technique itself seems to encode some cultural knowledge, which is presumably why even providing the details might seem culturally invasive--because such knowledge isn't intended for outsiders, except unless taught by a member.

swiley 5y ago

Yeah, a lot of people don't realize you can't compare intervals of UTC seconds without an almanac generated by a random natural process.

vikiomega9 5y ago

> for instance, above normal fresh water accumulation on land will measurably change the length of a day Is there a name for this that I can google for?

echelon 5y ago
I was curious: https://en.wikipedia.org/wiki/Day_length_fluctuations https://en.wikipedia.org/wiki/Day_length_fluctuations
HPsquared 5y ago
The general physics concept is moment of inertia. If water is moved uphill, this redistributes some of the Earth's mass further away from the axis of rotation, which increases its moment of inertia. Since the total angular momentum of the Earth is not changed by doing this, the result is a reduction of the angular velocity, in other words lengthening the day. NASA calculated, for instance, that filling the Three Gorges Dam reservoir would lengthen the day by 0.06 microseconds.
- swader999 5y ago
  I wondered why the days felt longer. Thanks.

dmoy 5y ago

The time smear (not skew, really) method works very, very well, for almost everything Here's as pretty good summary: https://developers.google.com/time/smear https://developers.google.com/time/smear