A reference time describes what standard of time we use. On Earth, for most human use cases, the reference time is UTC. UTC is measured by using International Atomic Time (TAI, from the French "temps atomique international") and adding or subtracting a prescribed number of leap seconds to account for the rotation of the Earth.
We don't use TAI in everyday use because it's constantly and continuously changing in small ways to account for the tiny accelerations or decelerations in Earth's rotation, and that's annoying for computers. So instead we use UTC.
A time zone is a different thing entirely. A time zone is a set of rules that describes how to convert from a reference time to a local time.
Most people think of a time zone as being a fixed offset, like "I use Eastern Time; that means UTC-5". This is wrong. A time zone is a _set_ of offsets, each of which applies to a _range_ of reference times. For example, we have a time zone called "America/New York". This describes, for any current or future datetime in reference time, what the correct _local_ time would be.
Here the scientists are doing two things: deciding what the UTC equivalent for the Moon should be (the reference time) and deciding what (if any) offsets should be applied to compute "local" time somewhere on the Moon (the time zone).
> We don't use TAI in everyday use because it's constantly and continuously changing in small ways to account for the tiny accelerations or decelerations in Earth's rotation, and that's annoying for computers. So instead we use UTC.
Wait, what? TAI is the one time standard that doesn't change. It's just a bunch of atomic clocks averaged together. As monotonic as human kind is able to manufacture, at this time.
UTC is TAI+varying offset in an effort to stay close to mean solar time.
The varying offset of UTC, called leap seconds, is what's annoying to computers. If we ran computers on TAI, they would be simpler!
And "data center time" tends to be something approximating UTC, with leap seconds smeared into continuous adjustments, just because UTC is annoying to computers.
> Wait, what? TAI is the one time standard that doesn't change. It's just a bunch of atomic clocks averaged together. As monotonic as human kind is able to manufacture, at this time.
That is not the complete story. The calculation used to average the clocks has changed over time, thus amending TAI. The "perfect monotonic" time you're talking about is TT (terrestrial time), not TAI.
Wikipedia about TT: "It is a theoretical ideal, and real clocks can only approximate it. [...] TT is indirectly the basis of UTC, via International Atomic Time (TAI)."
So, TAI is what we are able to measure. TT is a theoretical construct. Can't run computers on TT, can run them on TAI.
We don't use TAI in everyday use because it's constantly and continuously changing in small ways to account for the tiny accelerations or decelerations in Earth's rotation, and that's annoying for computers. So instead we use UTC.
A time zone is a different thing entirely. A time zone is a set of rules that describes how to convert from a reference time to a local time.
Most people think of a time zone as being a fixed offset, like "I use Eastern Time; that means UTC-5". This is wrong. A time zone is a _set_ of offsets, each of which applies to a _range_ of reference times. For example, we have a time zone called "America/New York". This describes, for any current or future datetime in reference time, what the correct _local_ time would be.
Here the scientists are doing two things: deciding what the UTC equivalent for the Moon should be (the reference time) and deciding what (if any) offsets should be applied to compute "local" time somewhere on the Moon (the time zone).