11 ms·

Wouldn't be easier to just calibrate the clocks and use UTC?

rob74 3y ago
My thought exactly - the fact that time runs slightly faster on the Moon than on Earth is fascinating, but the pragmatic approach would be to just compensate for the deviation.
- lxgr 3y ago
  How would you? Periodic leap seconds, or redefine the second (which would have impacts on many other units of measurements derived from it – are you prepared to also introduce lunar meters, for example)?
  - rob74 3y ago
    The compensation for the relativistic effects just makes sure that the second on the Moon is the same as the second on Earth. According to the article another commenter linked (https://www.ipses.com/eng/in-depth-analysis/standard-of-time-definition/ https://www.ipses.com/eng/in-depth-analysis/standard-of-time...) this is already routinely done on GPS satellites: > the only corrections made on atomic clocks located on satellites are very small adjustments to ensure that they remain perfectly synchronized with atomic clocks installed on the Earth (usually to correct drifts due to relativistic effects). this takes care of the effect mentioned in the article. However the more relevant (and debatable) question is if "Moon time" should also observe the leap seconds (which are introduced to account for variations in Earth's rotation, so have nothing to do with the Moon).
    - lxgr 3y ago
      This only works on the GPS satellites because they provide the GPS time for Earth's benefit, not their own. For all internal operations requiring high precision, they'd actually have to keep their own time reference (or calculate a dynamic offset from "GPS time") or they'd get unexpected results since the atomic clocks they carry run fast with regards to the SI definition of a second. (It could be the other way around, i.e. the clocks running correctly with regards to the satellite's frame of reference and an offset being applied to the signal, but I suspect skewing clocks to fit the Earth-based frame is easier.)
deleted 3y ago
[deleted]
marcosdumay 3y ago
And suddenly all of physics changes slightly.
- non-chalad 3y ago
  How often has this happened in the past? Has it had any effect?
  - withinboredom 3y ago
    Go back a couple hundred years before there were measures. A bolt from one foundry was a different size than the bolts in another foundry. It wasn't until the early 1900s that things were actually attempted to be standardized. Even until the '50s/'60s (and '70s in some countries), you'd often have to go to your local blacksmith to get them to make something as simple as a bolt.
zokier 3y ago
The actual policy has pretty clear explanation why LTC is needed: > Additionally, the navigation accuracy a system can achieve with signals from multiple space-based assets, such as a person navigating on Earth with signals from Global Positioning System satellites, depends on the synchronization of those assets with each other. At the Moon, synchronizing each lunar asset with an Earth-based time standard is difficult — due to relativistic effects, events that appear simultaneous at the Earth (e.g., the start of a broadcast signal) are not simultaneous to an observer at the Moon. ... > Precision applications such as spacecraft docking or landing will require greater accuracy than current methods allow ... > Beyond these operational challenges, the direct use of UTC at the Moon (i.e., without correction) as the local time scale would have cascading effects for applications that require precise metrology. International System of Units (SI) core unit definitions, including the meter and kilogram, rely on the SI definition of time. Due to relativistic effects, a non-SI unit would introduce uncertainty in core unit definitions. These types of errors will have undesired impacts, such as reducing the accuracy of mapping and inertial navigation products
- aftbit 3y ago
  >due to relativistic effects, events that appear simultaneous at the Earth (e.g., the start of a broadcast signal) are not simultaneous to an observer at the Moon. Isn't this true on Earth as well, just to a slightly lesser degree? Why are the synchronization mechanisms used to correct for drift in LEO suddenly unable to cope when used on Luna?
  - CuriousCosmic 3y ago
    It's true for exactly the same reason. You have - TAI: i.e. Atomic time which is basically the aggregate of a bunch of major atomic clocks to get as close as possible to "true time" on earh. - UT: i.e. Universal Time on earth with the different UT0, UT1, etc providing different levels of correction based on where you are on earth. - UTC: i.e. coordinated time that is the same anywhere on earth. This is derived from TAI but receives leap seconds when it is sufficiently out of sync from UT1. - GPS time: i.e. the specific time standard kept on GPS satellites based on their orbit. This time is derived from UTC(UNSO) which is a specific UTC clock at the US Naval Observatory and the offsets are recorded by the satellites. So you have your GPS time and your UTC time. What this proposal is doing is effectively the same thing. i.e. creating a new coordinated time standard for the moon (LTC) that tracks an offset of how far it's drifted from UTC so you can effectively coordinate. And eventually when the moon gets it's own GPS (which it will eventually), you'll have GPS(LTC), i.e. GPS time relative to LTC.
ISL 3y ago
To do so is to redefine the second on the moon. That redefines the Watt, the Joule, the Newton, the Ampere, the Pascal, the Becquerel, etc. It even makes a voltmeter read incorrectly. Moon-meters would be different from Earth-meters. Careful.
- doublerabbit 3y ago
  How many moon metres equate to 10 space football fields?
  - 8338550bff96 3y ago
    The size of football fields might need to change as well to accommodate the change in play style. You probably don't want quarterbacks dunking a touchdown in one flying leap from the 50-yard line.
    - kube-system 3y ago
      > You probably don't want quarterbacks dunking a touchdown in one flying leap from the 50-yard line. That’s exactly what I want! takeMyMoney.jpg
    - dmd 3y ago
      Jon Bois has you covered
    - non-chalad 3y ago
      Is that moon yards, or space yards?
      - saalweachter 3y ago
        Is it space feet, or space survey feet?
        Findecanor 3y ago
        It has been speculated that humans evolved in lower gravity would grow taller, getting longer finer features than humans on earth. If an independence movement on Luna gets hold, it might want to differentiate Luna from Earth, and introduce a "lunar foot" based on lunar people.

My thought exactly - the fact that time runs slightly faster on the Moon than on Earth is fascinating, but the pragmatic approach would be to just compensate for the deviation.

lxgr 3y ago
How would you? Periodic leap seconds, or redefine the second (which would have impacts on many other units of measurements derived from it – are you prepared to also introduce lunar meters, for example)?
- rob74 3y ago
  The compensation for the relativistic effects just makes sure that the second on the Moon is the same as the second on Earth. According to the article another commenter linked (https://www.ipses.com/eng/in-depth-analysis/standard-of-time-definition/ https://www.ipses.com/eng/in-depth-analysis/standard-of-time...) this is already routinely done on GPS satellites: > the only corrections made on atomic clocks located on satellites are very small adjustments to ensure that they remain perfectly synchronized with atomic clocks installed on the Earth (usually to correct drifts due to relativistic effects). this takes care of the effect mentioned in the article. However the more relevant (and debatable) question is if "Moon time" should also observe the leap seconds (which are introduced to account for variations in Earth's rotation, so have nothing to do with the Moon).
  - lxgr 3y ago
    This only works on the GPS satellites because they provide the GPS time for Earth's benefit, not their own. For all internal operations requiring high precision, they'd actually have to keep their own time reference (or calculate a dynamic offset from "GPS time") or they'd get unexpected results since the atomic clocks they carry run fast with regards to the SI definition of a second. (It could be the other way around, i.e. the clocks running correctly with regards to the satellite's frame of reference and an offset being applied to the signal, but I suspect skewing clocks to fit the Earth-based frame is easier.)

deleted 3y ago

[deleted]

marcosdumay 3y ago

And suddenly all of physics changes slightly.

non-chalad 3y ago
How often has this happened in the past? Has it had any effect?
- withinboredom 3y ago
  Go back a couple hundred years before there were measures. A bolt from one foundry was a different size than the bolts in another foundry. It wasn't until the early 1900s that things were actually attempted to be standardized. Even until the '50s/'60s (and '70s in some countries), you'd often have to go to your local blacksmith to get them to make something as simple as a bolt.

zokier 3y ago

The actual policy has pretty clear explanation why LTC is needed: > Additionally, the navigation accuracy a system can achieve with signals from multiple space-based assets, such as a person navigating on Earth with signals from Global Positioning System satellites, depends on the synchronization of those assets with each other. At the Moon, synchronizing each lunar asset with an Earth-based time standard is difficult — due to relativistic effects, events that appear simultaneous at the Earth (e.g., the start of a broadcast signal) are not simultaneous to an observer at the Moon. ... > Precision applications such as spacecraft docking or landing will require greater accuracy than current methods allow ... > Beyond these operational challenges, the direct use of UTC at the Moon (i.e., without correction) as the local time scale would have cascading effects for applications that require precise metrology. International System of Units (SI) core unit definitions, including the meter and kilogram, rely on the SI definition of time. Due to relativistic effects, a non-SI unit would introduce uncertainty in core unit definitions. These types of errors will have undesired impacts, such as reducing the accuracy of mapping and inertial navigation products

aftbit 3y ago
>due to relativistic effects, events that appear simultaneous at the Earth (e.g., the start of a broadcast signal) are not simultaneous to an observer at the Moon. Isn't this true on Earth as well, just to a slightly lesser degree? Why are the synchronization mechanisms used to correct for drift in LEO suddenly unable to cope when used on Luna?
- CuriousCosmic 3y ago
  It's true for exactly the same reason. You have - TAI: i.e. Atomic time which is basically the aggregate of a bunch of major atomic clocks to get as close as possible to "true time" on earh. - UT: i.e. Universal Time on earth with the different UT0, UT1, etc providing different levels of correction based on where you are on earth. - UTC: i.e. coordinated time that is the same anywhere on earth. This is derived from TAI but receives leap seconds when it is sufficiently out of sync from UT1. - GPS time: i.e. the specific time standard kept on GPS satellites based on their orbit. This time is derived from UTC(UNSO) which is a specific UTC clock at the US Naval Observatory and the offsets are recorded by the satellites. So you have your GPS time and your UTC time. What this proposal is doing is effectively the same thing. i.e. creating a new coordinated time standard for the moon (LTC) that tracks an offset of how far it's drifted from UTC so you can effectively coordinate. And eventually when the moon gets it's own GPS (which it will eventually), you'll have GPS(LTC), i.e. GPS time relative to LTC.

ISL 3y ago

To do so is to redefine the second on the moon. That redefines the Watt, the Joule, the Newton, the Ampere, the Pascal, the Becquerel, etc. It even makes a voltmeter read incorrectly. Moon-meters would be different from Earth-meters. Careful.

doublerabbit 3y ago
How many moon metres equate to 10 space football fields?
- 8338550bff96 3y ago
  The size of football fields might need to change as well to accommodate the change in play style. You probably don't want quarterbacks dunking a touchdown in one flying leap from the 50-yard line.
  - kube-system 3y ago
    > You probably don't want quarterbacks dunking a touchdown in one flying leap from the 50-yard line. That’s exactly what I want! takeMyMoney.jpg
  - dmd 3y ago
    Jon Bois has you covered
  - non-chalad 3y ago
    Is that moon yards, or space yards?
    - saalweachter 3y ago
      Is it space feet, or space survey feet?
      - Findecanor 3y ago
        It has been speculated that humans evolved in lower gravity would grow taller, getting longer finer features than humans on earth. If an independence movement on Luna gets hold, it might want to differentiate Luna from Earth, and introduce a "lunar foot" based on lunar people.