5 ms·

Having each day be 3 minutes longer/shorter than the previous one is pretty crazy, even if it's mitigated by the fact that 1 Venusian day is ~243 Earth days. T

Having each day be 3 minutes longer/shorter than the previous one is pretty crazy, even if it's mitigated by the fact that 1 Venusian day is ~243 Earth days. That really makes me wonder how timekeeping would work for civilizations that evolved on planets with variable day length. Earth has variable periods of sunlight depending on latitude, but Earth's day length itself is relatively constant.

tintor 5y ago
Water clocks and sand clocks could still work, or some other periodic natural phenomena (like moon phases).
cdumler 5y ago
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
sandworm101 5y ago
Start the clock at zero and just start counting seconds. The problem only occurs when you are trying to calculate sunrise/set times. Your solar power system doesn't care about leap seconds/days/years. It knows to expect sunrise at 353478515 seconds without regard for human concepts of a particular day or month.
- munk-a 5y ago
  Well I assume the drift based on atmospheric anomalies doesn't tend toward a total delta of +/- 0 over time - or at least we're not accurately accounting for it yet. As such we'd face the same january in summer problem the romans faced right? Slowly midnight will move further and further from the time when you're furthest from the sun.
BitwiseFool 5y ago
I'm imagining a system where you have two different lengths of time units. You can have a "scientific second" which is defined by distance and the speed of light. Just like we have now in SI. When the rotation of the planet changes slightly you need to compensate by adding leap seconds every few years for things to sync up. Eventually they will need to add a leap second every day as the earth's rotation slows down. Some planet with high variation would be adding and removing these frequently. But, you can define a second as 1/86400th of a "day". For most civil purposes you just want to know when an event happened relative to the day/night cycle and the year. In which case the order of events is more important than the precise amount of time between the events. If precision is needed, you can always measure in scientific seconds and convert accordingly. I figure the "civil second" is fine for such a purpose because it's not like living beings can consistently and accurately keep track of time in their heads. Now for a planet with a rotation as slow as Venus the concept of a "day" is probably meaningless. It would be more like a season of light and darkness. So I suppose you'd just only use scientific seconds and count upwards?
- brandmeyer 5y ago
  Turns out that this standard already exists. UT1 (and its close cousin UT1R) track Earth's rotation using radio astronomy techniques. The basis for adding leap seconds is the wind up between UTC and UT1. I agree, we ought to align UTC to UT1 instead of TAI. Doing so is not trivial on a technical level, though. At the very least, the GNSS broadcast time parameters wouldn't support such a revision for decades.
harywilke 5y ago
Interesting. Noon is when the sun is highest. I had fun explaining time zones to my son the other day. I think he got lost in my train analogy: If the train travels around the earth at the same speed the earth turns, then it's always noon on the train.
- ArnoVW 5y ago
  Conceptual stuff like that is tricky if you don't already know it. I've found that visual explanation works best for building an intuition. My approach for day / night type of questions: - a soccer ball - a toilet roll - the lamp in your phone When you shine your lamp through the toilet roll on the ball, you get a neat 'terminator'.
Pxtl 5y ago
It gets better. Venus' atmosphere superrotates far faster and so an airship city over Venus would have a different day/night cycle too.

tintor 5y ago

Water clocks and sand clocks could still work, or some other periodic natural phenomena (like moon phases).

cdumler 5y ago

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

sandworm101 5y ago

Start the clock at zero and just start counting seconds. The problem only occurs when you are trying to calculate sunrise/set times. Your solar power system doesn't care about leap seconds/days/years. It knows to expect sunrise at 353478515 seconds without regard for human concepts of a particular day or month.

munk-a 5y ago
Well I assume the drift based on atmospheric anomalies doesn't tend toward a total delta of +/- 0 over time - or at least we're not accurately accounting for it yet. As such we'd face the same january in summer problem the romans faced right? Slowly midnight will move further and further from the time when you're furthest from the sun.

BitwiseFool 5y ago

I'm imagining a system where you have two different lengths of time units. You can have a "scientific second" which is defined by distance and the speed of light. Just like we have now in SI. When the rotation of the planet changes slightly you need to compensate by adding leap seconds every few years for things to sync up. Eventually they will need to add a leap second every day as the earth's rotation slows down. Some planet with high variation would be adding and removing these frequently. But, you can define a second as 1/86400th of a "day". For most civil purposes you just want to know when an event happened relative to the day/night cycle and the year. In which case the order of events is more important than the precise amount of time between the events. If precision is needed, you can always measure in scientific seconds and convert accordingly. I figure the "civil second" is fine for such a purpose because it's not like living beings can consistently and accurately keep track of time in their heads. Now for a planet with a rotation as slow as Venus the concept of a "day" is probably meaningless. It would be more like a season of light and darkness. So I suppose you'd just only use scientific seconds and count upwards?

brandmeyer 5y ago
Turns out that this standard already exists. UT1 (and its close cousin UT1R) track Earth's rotation using radio astronomy techniques. The basis for adding leap seconds is the wind up between UTC and UT1. I agree, we ought to align UTC to UT1 instead of TAI. Doing so is not trivial on a technical level, though. At the very least, the GNSS broadcast time parameters wouldn't support such a revision for decades.

harywilke 5y ago

Interesting. Noon is when the sun is highest. I had fun explaining time zones to my son the other day. I think he got lost in my train analogy: If the train travels around the earth at the same speed the earth turns, then it's always noon on the train.

ArnoVW 5y ago
Conceptual stuff like that is tricky if you don't already know it. I've found that visual explanation works best for building an intuition. My approach for day / night type of questions: - a soccer ball - a toilet roll - the lamp in your phone When you shine your lamp through the toilet roll on the ball, you get a neat 'terminator'.

Pxtl 5y ago

It gets better. Venus' atmosphere superrotates far faster and so an airship city over Venus would have a different day/night cycle too.