Gregory's ServerI keep seeing the news about lunar time presented as βthe Moon is getting its own time zone." What's actually happening is the Moon is getting its own time *standard*. The problem being solved is that time passes slightly more quickly on the Moon compared to Earth (due to General Relativity) and so the Moon needs its own time standard for precise measurements and navigation. UTC is the time standard for measuring time on Earth, and LTC is being created for the Moon.
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@foolishowl General relativity and quantum mechanics both have a way of doing that! @dgoldsmith Given that UTC stands for Coordinated Universal Time (at least in English), it seems like it's in need of a renaming. Perhaps Coordinated Terrestrial Time? I wonder if this will continue for other important celestial bodies? I wouldn't be surprised if at least Mars got its own time standard codified. Wikipedia mentions an "MTC", but only as a "proposed" standard based on Mars's orbit instead of atomic clocks. @dgoldsmith Although it feels a little impractical to keep creating new standards for every celestial body we visit, perhaps we need a new standard somehow independent of general relativity... how about "Stardate"? π @michaelbradley I don't think we're going to be visiting that many celestial bodies, so I'm not worried about that. You still need to define the relationship between the various time standards. UTC is basically "stardate" already; LTC will be defined relative to UTC. @michaelbradley @dgoldsmith @pglpm @michaelbradley Great paper! I'd never heard of the journal before. @dgoldsmith - thatβs a great link, after reading the page twice Iβm sure I donβt fully appreciate/understand the topic. However this line has zapped my brainβ¦.. βRelative to Earth's age in billions of years, Earth's core is in effect 2.5 years younger than its surfaceβ @ianbradbury The planet orbiting the black hole in βInterstellar" is an extreme example (if you've seen that, or know the plot).  @dgoldsmith I'm really not sure that replacing MET is needed just yet, but it's a very optimistic move. (MET, as you probably know, is mission elapsed time, which has been fine and will remain fine until we have satellites around the moon or other long term presence.) @adamshostack I don't think it's really needed for the function that MET serves, but more to have a standard to coordinate multiple spacecraft/experiments/instruments/etc. Yes, it's a bit forward-thinking. @dgoldsmith Exactly. If you need to coordinate stuff, that's exciting ... times. Sorry. I couldn't resist. :blobangel:  @dgoldsmith You seem to be knowledgeable on this topic. Could you explain why we do not just compensate for gravitational red shift on the moon the same way we do for the various NMI labs that are at different altitudes and thus run at slightly different rates? Why do we need LTC when just using UTC with the correct definition of the second (i.e. defined at zero gravitational field) would be sufficient? @hattifattener @TheDarcBird Nowadays most people use "GMT" to mean the time zone "UTC+0β, but it has other meanings. Details here: https://en.wikipedia.org/wiki/Greenwich_Mean_Time  Wait, time passes more quickly on the moon? How does that work? Is it something influenced by planetary gravity? @trabex It's called βgravitational time dilation" (https://en.wikipedia.org/wiki/Gravitational_time_dilation). Time passes more slowly in a gravitational field. The stronger the gravity, the slower time passes. It's a consequence of general relativity. So time passes more slowly on Earth than on the Moon because Earth's gravity is stronger. On Earth, time passes more quickly at the top of a mountain than at sea level. This effect has been measured. |
@dgoldsmith It's kind of mindblowing.