I keep seeing the news about lunar time presented as “the 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.
@trabex It's called “gravitational 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 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?
If you're curious why time passes more quickly on the Moon, it's this: https://en.wikipedia.org/wiki/Gravitational_time_dilation Because Earth's gravity is higher, there’s more time dilation than on the Moon (by about 58.7 microseconds per day, or 2.144 seconds per century).
One way to think about it is that the local neighborhood of spacetime for someone standing on the Earth's surface is boosted (“tilted”, in a 4D sense) relative to that for someone far away from any massive body.
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