12 ms·

Unix time is not really great for any scientific purpose; it defines each day to have exactly 86400 seconds. (So, eventually you have problems with leap second

Unix time is not really great for any scientific purpose; it defines each day to have exactly 86400 seconds. (So, eventually you have problems with leap seconds.) UTC is better, because at least it is aware of leap seconds, but performing any calculation spanning a year's end involves consulting a database of leap seconds. Notably these aren't determined much in advance, so such calculations involving future dates will also involve leap-second errors. TAI is best (for non-relativistic non-sidereal purposes), as it is not adjusted to account for leap seconds. You can calculate with it without trouble. (All three of the above are based on the atomic SI second, so despite their differences, their seconds tick synchronously.)

spiffytech 6y ago
In astronomical contexts there are good alternatives to the epoch (like TDB, mentioned in another comment). I interpreted the top-level question as relating to day-to-day measurements and representations of time, presumably for use by extraterrestrial humans, since the commenter asked in the context of handling time zones and units like weeks and months which are irrelevant in a scientific context. UTC is not a great choice for a universal interplanetary time system, as it's designed to work on just one planet, for just one calendar system. It'll work fine while we're asking humans on Earth to oversee robots on the Mars, but will fall down pretty quickly once humans take permanent residence on celestial bodies that don't have Earth's rhythms.
fogihujy 6y ago
Well, the general idea seems usable enough; X time units from a specific reference point. Conversion is then done to whatever local time-keeping system you might have. Leap seconds are based on conditions here on Earth and wouldn't really be needed on Mars or Venus. They might have different peculiarities though, and they wouldn't be usable on Earth. In that situation, a single point of reference would be useful for conversions.
- colanderman 6y ago
  Right; "X time units from a specific reference point" is what TAI is. Taking Unix time and removing the notion of leap seconds is effectively a circumlocution for exactly that standard :)

spiffytech 6y ago

In astronomical contexts there are good alternatives to the epoch (like TDB, mentioned in another comment). I interpreted the top-level question as relating to day-to-day measurements and representations of time, presumably for use by extraterrestrial humans, since the commenter asked in the context of handling time zones and units like weeks and months which are irrelevant in a scientific context. UTC is not a great choice for a universal interplanetary time system, as it's designed to work on just one planet, for just one calendar system. It'll work fine while we're asking humans on Earth to oversee robots on the Mars, but will fall down pretty quickly once humans take permanent residence on celestial bodies that don't have Earth's rhythms.

fogihujy 6y ago

Well, the general idea seems usable enough; X time units from a specific reference point. Conversion is then done to whatever local time-keeping system you might have. Leap seconds are based on conditions here on Earth and wouldn't really be needed on Mars or Venus. They might have different peculiarities though, and they wouldn't be usable on Earth. In that situation, a single point of reference would be useful for conversions.

colanderman 6y ago
Right; "X time units from a specific reference point" is what TAI is. Taking Unix time and removing the notion of leap seconds is effectively a circumlocution for exactly that standard :)