Lunar Time

Not only do you need leap seconds to keep solar time and atomic time in sync, you'll need a different kind of leap second to keep Lunar atomic time and Earth atomic time in sync, because mass distorts spacetime.

So good luck with that...

Defining lunar time is not simple:

Although the definition of the second is the same everywhere, the special theory of relativity dictates that clocks tick slower in stronger gravitational fields. The Moon's gravitational pull is weaker than Earth's, meaning that, to an observer on Earth, a lunar clock would run faster than an Earth one. Gramling estimates that a lunar clock would gain about 56 microseconds over 24 hours. Compared with one on Earth, a clock's speed would also subtly change depending on its position on the lunar surface, because of the Moon's rotation, says Tavella. "This is a paradise for experts in relativity, because you have to take into account so many things," she adds.

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21 Responses:

  1. Steve Allen says:

    The tides at the beach are telling us that neither do atomic chronometers on the surface of the earth always tick at the same rate.

    • tfb says:

      They do always tick at the same rate.  It's just that the curves they follow through spacetime have different lengths.

      That sounds like nitpicking but it's not: clocks whose timekeeping is controlled by gravity (which really means pendulum clocks) have rates which do vary as the local gravitational field varies, while atomic clocks don't (or, well, they probably do but you'd only be able to notice if you were in some field where tidal effects are a big deal on atomic scales, which probably means close to the event horizon of a (small) black hole).

  2. jwilkes says:

    Why don't we just start with the CVE's we'd like to see from this.

    Then we can work backwards to build the appropriate moontime libraries needed to trigger them.

    • jwz says:

      Given that there is a sizable contingent of people taking the position of "leap seconds are weird, let's just get rid of them, yolo" I don't think that's going to go very well.

      • Big says:

        I am looking forward to hearing about the timely death of the first manned Mars mission along with both the CEO and the entire cargo of indentured slave fan boys when the ship plummets into the Martian surface due to missing leap seconds and relativistic time corrections in the “totally hardcore” flight guidance software.

        • MattyJ says:

          We've already sent things safely to mars ...

          • phuzz says:

            Yes, but what's more useful to humanity to land safely on Mars, a robot, or a billionaire?

            • jwz says:

              Hard to say! Let's send a couple dozen of each and see which one lasts longest.

              • phuzz says:

                As long as we don't have to bring them back.

              • tfb says:

                Let's not.  It's almost inconceivable that billionaires and their slave crews can be made sterile enough not to seriously fuck with our chances of knowing if Mars has life.  Of course plutocrats don't care about that: the only life they care about is their own.

                I propose instead that we encourage them to aim at the Sun.  It's unfortunate that the huge delta v requirement makes landing on the Sun much harder than Mars.  But I am sure they will be up to the challenge.

              • Marcus says:

                Pfft.  To this day, only the Soviets have landed a craft on Venus.  I feel like we should take Venus back with a manned mission as you suggest.

            • MattyJ says:

              A. As many billionaires as possible.

      • Rodger says:

        There are a disturbing number of brogrammers who think time zones are too hard and we shouldn’t have them.

        • derpatron9000 says:

          Please take all appropriate action available to remove commit bits from such dopes

        • thielges says:

          TZs are indeed hard.  Everyone who can leverage an existing maintained TZ package should leverage reuse and avoid coding anew.

          The difficulty of TZs isn't technical.  Instead it is a matter of discovering and implementing constantly changing requirements.  When any government agency, even one subordinate to the national sovereign, can change their rules at any time and announce their change via their own chosen official channels (which might not even involve publication on the internet) then finding about the recent TZ changes can be quite an Easter egg hunt.                                       

  3. Mark says:

    That would be the general theory of relativity, not the special theory.  Special relativity says nothing about gravity.

    Not remotely an important point, but you'd hope for better attention to scientific detail from this particular venue.

  4. BHN says:

    This is probably going to drive the tzlist denizens nuts.

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