Atheism

Days are local to the object: moon or planet.

Years... Also local.

There will be conversion factors and differing methods to note time. Gregorian works just fine if we do the occasional extra skip and we have thousands of years to find out how higher ocean levels change the rate of change.

Honestly great write up…

But going with the easy way out— we’d end up having 2…. Maybe. The people on Planet X would need a earth calendar to keep track of things back in mission control; and you’d have the local calendar for local things

Similar to how the mars rover teams do now. While the mission follows mars time; they live on earth.

So depending on what you do; you’d likely have two watches or clocks and calendars.

Great analysis, but you're making it way more complicated than it is.

We are entrenched with the Gregorian calendar. The same way we are entrenched with the 12/24hr clock, decimal counting system, etc.

Any planet that needs a calendar will have their own based on the planet's orbit and rotation, but they will still be tied to the earth calender for as long as they are in contact with earth.

Ditch days, months, years; at least in space. Enjoy the second.

We currently use three primary units of time: day, month, year. They don't divide well by each other, as shown in your post, but since they refer to things that we experience, they're still useful.

Outside Earth, however, they lose meaning. So might as well ditch all of them, and stick to the nearest of a standard that we got - a day divided by 24, then 60, then 60. Also known as "the second". Then just measure things by that; for example Darwin was around 2.3 Gs old when he died (73y; a gigasecond is around 32y).

Then all that's left is deciding on an origin. The start of the Holocene is fine, but so is anything else. Even mythological - as long as people agree on when Kronos castrated Ouranos, you could use it as the origin if you wanted.

And developers thought timezones are hard now...

Pfft amateurs

Because there is lower gravity on the moon than on Earth, time there moves slightly faster — 58.7 microseconds faster every day.

https://www.space.com/white-house-nasa-time-zone-moon

"Day" and "year" have local equivalents for any orbiting, revolving body. We'd probably retain the second as the basic unit of time and maybe go to something like decimal time as a generic standard for communicating between places and for trade and business. That covers spans of time. For absolute time, we may be out of luck. Even assuming we could pick a standard object and point in time as anchors, relativity means that each frame of reference has clocks moving at their own speeds. So far as we know, there is no universal frame of reference.

So even if we said "every revolution of the pulsar at coordinates blahblahblah is one galactic standard day and we define Year 0 as starting exactly 3237.95 standard days ago" we still wouldn't have a universal time standard because people close to black holes will have seen fewer rotations of the pulsar, so they'd be living in the pasts of any planets in a faster frame of reference.

We already use time zones on earth which alter depending on our relationship with the earth tilt and rotation. I imagine well dontge same. Well use earth time as a reference and adjust our 'time zone' to life away from earth.

Obviously, if another time system makes sense in another place, wed adapt to that specific place, but I think it would still be referenced to earth time.

Should we meet others with different measuring systems, maybe wed have to adapt ours and theirs to be mutually comprehensible but similarly, I don't think we would change of still using a circadian rhythm for life.

You're asking like three different questions in one.

• What is year one? (You mentioned the Holocene calendar)
• When are leap years? (Proleptic Gregorian calendar)
• What day/month system works on other planets?

The answers to these are,

• It doesn't matter what we call year one. It's a bike shedding argument ultimately. Perhaps year one on another planet is the year it is colonized.
• Planets may or may not need leap years, depending on the ratio of days to years.
• Each planet would likely have its own day/month system because their orbits are so different.

All dates would have a conversion to earth dates or something like Julian star dates (as opposed to Julian accounting dates which is just the day of the year). In the same way we convert local timezones to others or UTC, we'd have the same concept for interplanetary communication. In the same way there are some people who (in my opinion foolishly) advocate to stop using timezones, some people may argue to use Julian (star) dates for all time based communication and to never use days, months, years, etc. again.

If the gravity is different enough, having a calendar that keeps track of both local and distant time would become a nightmare.