6 ms·

Is anyone aware of a date/time representation system that would work universally (including extraterrestrial places)? I just have been curious about this quest

by Seb-C 6y ago

Is anyone aware of a date/time representation system that would work universally (including extraterrestrial places)? I just have been curious about this question for long. Sure, we could keep an earth referential on a moon base, but then what about Mars? As a software developer it is already difficult to always get dates/times properly with timezones, now imagine places which does not have 24 hours per day or the same weeks/months/years durations...

timdux 6y ago
Mars calendar, each year has 24 months: https://en.wikipedia.org/wiki/Darian_calendar https://en.wikipedia.org/wiki/Darian_calendar Solar system time: https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time
- throw0101a 6y ago
  Alternatively: * https://www.kimstanleyrobinson.info/content/martian-calendar https://www.kimstanleyrobinson.info/content/martian-calendar See also: * https://en.wikipedia.org/wiki/Timekeeping_on_Mars https://en.wikipedia.org/wiki/Timekeeping_on_Mars
wh313 6y ago
There's Barycentric Dynamical Time, which takes time dilation into account: https://en.m.wikipedia.org/wiki/Barycentric_Dynamical_Time https://en.m.wikipedia.org/wiki/Barycentric_Dynamical_Time NASA has actually thought through this problem and created SPICE, which lets you convert between different time systems, some relativistic and some not, as well as doing conversions between various reference frames: https://naif.jpl.nasa.gov/naif/index.html https://naif.jpl.nasa.gov/naif/index.html
- dr_orpheus 6y ago
  SPICE is pretty awesome. I wish that more people in the aerospace industry were aware of, including people AT NASA. I work at a company contracting on NASA projects and a couple weeks ago I had to correct their code because they weren't accounting for the leap second offset between UTC and GPS correctly. When I asked why he wrote his own function instead of using SPICE he responded "what's SPICE?". Literally people in the same building as him maintain the SPICE toolkits.
  - sushicalculus 6y ago
    Need to bring back some of those brownbag lunch & learn events, starting with "SPICE up your clocks"! Except people might not be comfortable sitting in the same room these days
    - azinman2 6y ago
      No reason you can’t have virtual tech talks
    - 0xffff2 6y ago
      Comfort won't be much of a factor since most NASA centers are completely work from home for non-mission-critical work for the indefinite future. Nonetheless, we do have a ton of these kinds of things going on all the time. The bigger problem is that NASA's culture is so meeting heavy that it's hard to justify these kinds of low importance events on my calendar.
      - whoisthemachine 6y ago
        > The bigger problem is that NASA's culture is so meeting heavy that it's hard to justify these kinds of low importance events on my calendar. Not sure if you are speaking from experience, but if that is the case, and this is true, then NASA as an organization seems to be a poor judge of what's important.
        0xffff2 6y ago
        Yes, from experience. It's not that we don't know what's important, it's that it's all important and I have to find time to actually write code every now and then too. The real problem is just that we're all very busy and it's not really possible for everyone in the agency to have even a cursory awareness of everything that's going on. Even now with everything being virtual, I get invites to brown-bag type events probably 3-4 time per week. I can go to one or two, but there's no way I can fit every single one into my schedule.
- qz2 6y ago
  I have enough problems dealing with time on this planet. This is going to break a lot of software and software developers instantly :)
  - deleted 6y ago
    [deleted]
  - peterburkimsher 6y ago
    https://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25326999628/falsehoods-program... I'm very thankful for the creators of https://www.worldtimebuddy.com/ https://www.worldtimebuddy.com/ handling time zone weirdness, etc, so that I can still get to Zoom calls on time (usually). I don't know how the Moment developers can ever think it's "done" - "We now generally consider Moment to be a legacy project in maintenance mode. It is not dead, but it is indeed done."
nabla9 6y ago
UT0 is the basis for other times derived from motion of stars or extragalactic radio sources. On the Moon and Earth you can just use UTC like ISS does.
wongarsu 6y ago
UTC works just fine, or TAI if you don't want to deal with leap seconds. (UTC is international atomic time (TAI) offset by leap seconds to keep in sync with earth's rotation) Once you get into relativistic effects you need something better, but for practical purposes UTC and TAI are just fine for the foreseeable future. The days just become a meaningless abstract concept.
spiffytech 6y ago
It depends on which layer you're asking about addressing. You can represent anything non-relatavistic on top of the Unix epoch, and it could be handled as simply as using alternate time zones. The big problems come from huge Earth assumptions about interval duration and interval sequencing being violated. A lunar day is 29.5 Earth days. Does the lunar calendar use solar days, and just have absurdly long weeks and years? Maybe the years are standard Earth length, they just don't use weeks or months. Does a lunar society have a shorter "not-day" that replaces the way Earth uses days, and now everything needs to handle this new unit of time? Do days still get measured as solar intervals, and we just decide it's okay for days to be longer than weeks on the moon, so it stays Tuesday for a month at a time?
- dsr_ 6y ago
  Off earth you have a launch criterion and accumulated subjective seconds. That's your onboard time. There are no days, weeks, months, years. Just count the seconds and make sure everyone knows the epoch you started at. Now, let's suppose you have a permanent settled outpost on Luna. You still use accumulated seconds as your time basis, but for casual conversation, you can talk about any Earth time marking that makes sense to you -- next Tuesday, or March 20th, or "in three months". You might occasionally care about whether it's bright or dark outside, but the tidal lock means that local weeks and months really aren't useful. The hard thing is when you actually care about both the time on Earth and the local time/date/season of a planet you are interacting with naturally. Let's hypothesize a terraformed Venus, and while we're at it, let's change the axial tilt from 2.mumble degrees to 24 degrees. That gives us a 224ish terrestrial day V-year, a 1.92 V-day V-year, and approximately eight seasons per V-year, each being 56 days long. On that planet, you get to go outside and enjoy the fresh air, but you want to know what season it is more than you want to know what month it is: dark-winter, dark-fall, dark-summer, dark-spring bright-winter, bright-fall, hell, bright-spring (Venus rotates backwards, that's why the seasons are all funny.) But when you want to know when the next shipment of Earth whisky is coming, you ask a computer.
  - 0xffff2 6y ago
    Mission elapsed time just complicates things. Now that we have enough memory that we don't need to worry so much about overflow, we just use the Unix epoch even onboard spacecraft.
LeoPanthera 6y ago
"International Atomic Time" (TAI) is probably the logical choice. It's the same as UTC, but without leap seconds. Maybe the "stardate" of the future will simply be Unix Time, but based on TAI.
ceejayoz 6y ago
Vernor Vinge's A Deepness in the Sky has a bit where a "programmer archaeologist" (a term I just love) notes that deep in the thousand year old code running the starship the time is still counted in seconds since about a megasecond after the first lunar landing.
fulafel 6y ago
Time dilation undoes hopes of making any measure work universally. (Unless you include a bunch of other things besides one number in the measure...) But for subjective time there's UT1 (UTC minus leap seconds).
- deleted 6y ago
  [deleted]
edem 6y ago
Ultraepoch? Milliseconds since the Big Bang?

by Seb-C 6y ago

timdux 6y ago

Mars calendar, each year has 24 months: https://en.wikipedia.org/wiki/Darian_calendar https://en.wikipedia.org/wiki/Darian_calendar Solar system time: https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time

throw0101a 6y ago
Alternatively: * https://www.kimstanleyrobinson.info/content/martian-calendar https://www.kimstanleyrobinson.info/content/martian-calendar See also: * https://en.wikipedia.org/wiki/Timekeeping_on_Mars https://en.wikipedia.org/wiki/Timekeeping_on_Mars

wh313 6y ago

There's Barycentric Dynamical Time, which takes time dilation into account: https://en.m.wikipedia.org/wiki/Barycentric_Dynamical_Time https://en.m.wikipedia.org/wiki/Barycentric_Dynamical_Time NASA has actually thought through this problem and created SPICE, which lets you convert between different time systems, some relativistic and some not, as well as doing conversions between various reference frames: https://naif.jpl.nasa.gov/naif/index.html https://naif.jpl.nasa.gov/naif/index.html

dr_orpheus 6y ago
SPICE is pretty awesome. I wish that more people in the aerospace industry were aware of, including people AT NASA. I work at a company contracting on NASA projects and a couple weeks ago I had to correct their code because they weren't accounting for the leap second offset between UTC and GPS correctly. When I asked why he wrote his own function instead of using SPICE he responded "what's SPICE?". Literally people in the same building as him maintain the SPICE toolkits.
- sushicalculus 6y ago
  Need to bring back some of those brownbag lunch & learn events, starting with "SPICE up your clocks"! Except people might not be comfortable sitting in the same room these days
  - azinman2 6y ago
    No reason you can’t have virtual tech talks
  - 0xffff2 6y ago
    Comfort won't be much of a factor since most NASA centers are completely work from home for non-mission-critical work for the indefinite future. Nonetheless, we do have a ton of these kinds of things going on all the time. The bigger problem is that NASA's culture is so meeting heavy that it's hard to justify these kinds of low importance events on my calendar.
    - whoisthemachine 6y ago
      > The bigger problem is that NASA's culture is so meeting heavy that it's hard to justify these kinds of low importance events on my calendar. Not sure if you are speaking from experience, but if that is the case, and this is true, then NASA as an organization seems to be a poor judge of what's important.
      - 0xffff2 6y ago
        Yes, from experience. It's not that we don't know what's important, it's that it's all important and I have to find time to actually write code every now and then too. The real problem is just that we're all very busy and it's not really possible for everyone in the agency to have even a cursory awareness of everything that's going on. Even now with everything being virtual, I get invites to brown-bag type events probably 3-4 time per week. I can go to one or two, but there's no way I can fit every single one into my schedule.
qz2 6y ago
I have enough problems dealing with time on this planet. This is going to break a lot of software and software developers instantly :)
- deleted 6y ago
  [deleted]
- peterburkimsher 6y ago
  https://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25326999628/falsehoods-program... I'm very thankful for the creators of https://www.worldtimebuddy.com/ https://www.worldtimebuddy.com/ handling time zone weirdness, etc, so that I can still get to Zoom calls on time (usually). I don't know how the Moment developers can ever think it's "done" - "We now generally consider Moment to be a legacy project in maintenance mode. It is not dead, but it is indeed done."

nabla9 6y ago

UT0 is the basis for other times derived from motion of stars or extragalactic radio sources. On the Moon and Earth you can just use UTC like ISS does.

wongarsu 6y ago

UTC works just fine, or TAI if you don't want to deal with leap seconds. (UTC is international atomic time (TAI) offset by leap seconds to keep in sync with earth's rotation) Once you get into relativistic effects you need something better, but for practical purposes UTC and TAI are just fine for the foreseeable future. The days just become a meaningless abstract concept.

spiffytech 6y ago

It depends on which layer you're asking about addressing. You can represent anything non-relatavistic on top of the Unix epoch, and it could be handled as simply as using alternate time zones. The big problems come from huge Earth assumptions about interval duration and interval sequencing being violated. A lunar day is 29.5 Earth days. Does the lunar calendar use solar days, and just have absurdly long weeks and years? Maybe the years are standard Earth length, they just don't use weeks or months. Does a lunar society have a shorter "not-day" that replaces the way Earth uses days, and now everything needs to handle this new unit of time? Do days still get measured as solar intervals, and we just decide it's okay for days to be longer than weeks on the moon, so it stays Tuesday for a month at a time?

dsr_ 6y ago
Off earth you have a launch criterion and accumulated subjective seconds. That's your onboard time. There are no days, weeks, months, years. Just count the seconds and make sure everyone knows the epoch you started at. Now, let's suppose you have a permanent settled outpost on Luna. You still use accumulated seconds as your time basis, but for casual conversation, you can talk about any Earth time marking that makes sense to you -- next Tuesday, or March 20th, or "in three months". You might occasionally care about whether it's bright or dark outside, but the tidal lock means that local weeks and months really aren't useful. The hard thing is when you actually care about both the time on Earth and the local time/date/season of a planet you are interacting with naturally. Let's hypothesize a terraformed Venus, and while we're at it, let's change the axial tilt from 2.mumble degrees to 24 degrees. That gives us a 224ish terrestrial day V-year, a 1.92 V-day V-year, and approximately eight seasons per V-year, each being 56 days long. On that planet, you get to go outside and enjoy the fresh air, but you want to know what season it is more than you want to know what month it is: dark-winter, dark-fall, dark-summer, dark-spring bright-winter, bright-fall, hell, bright-spring (Venus rotates backwards, that's why the seasons are all funny.) But when you want to know when the next shipment of Earth whisky is coming, you ask a computer.
- 0xffff2 6y ago
  Mission elapsed time just complicates things. Now that we have enough memory that we don't need to worry so much about overflow, we just use the Unix epoch even onboard spacecraft.

LeoPanthera 6y ago

"International Atomic Time" (TAI) is probably the logical choice. It's the same as UTC, but without leap seconds. Maybe the "stardate" of the future will simply be Unix Time, but based on TAI.

ceejayoz 6y ago

Vernor Vinge's A Deepness in the Sky has a bit where a "programmer archaeologist" (a term I just love) notes that deep in the thousand year old code running the starship the time is still counted in seconds since about a megasecond after the first lunar landing.

fulafel 6y ago

Time dilation undoes hopes of making any measure work universally. (Unless you include a bunch of other things besides one number in the measure...) But for subjective time there's UT1 (UTC minus leap seconds).

deleted 6y ago
[deleted]

edem 6y ago

Ultraepoch? Milliseconds since the Big Bang?