Introduction

I needed a way to record when events occur that is unambiguous, got annoyed with other time definitions making this difficult, things spiraled out of control, and I came up with Interstellar Time. It is designed, in part, to be fitting of the name.

Interstellar Time is based solely on seconds; it has no calendar since those are defined in connection with a planet. This means Interstellar Time has no need of leap seconds or days. In this way of thought, any time system that has a calendar and leap seconds is a planetary time system since it is intended to remain synchronized to the solar day and year of a planet. UTC is a perfect example. It includes leap seconds to use the correct definition of a second while staying in step with Earth's varying length days.

TAI, however, only started synchronized to the solar day of Earth, but has since advanced based on the definition of a second while still using a Terran calendar. This results in TAI becoming further desynchronized with Terran planetary time as UTC adds more leap seconds. Interstellar Time attempts to be more consistent by making no attempt to use the vestiges of planetary time while not using leap seconds. This should hypothetically make Interstellar Time an ideal intermediate form for converting between planetary time systems.

A number of computer systems use POSIX time, also called UNIX time. This time system is fixed to Earth's solar day, but uses a fixed length day. This is done by setting the clock back a second to account for a +1 leap second. The result is that using POSIX time for time stamps allows for two seconds of ambiguous time around a leap second. It also means that computations of durations can be incorrect unless extra effort is made to account for leap seconds.

Definition

Todo:: Determine if using Barycentric Coordinate Time (TCB) might be a better option, and if so, how to implement it.

The initial definition of Interstellar Time is intended to make it usable without being overly difficult. It is not intended to be a definition robust enough for use in interstellar travel, but hopefully a future revision of the definition will solve this issue. Interstellar Time is a count of seconds since time zero, which is arbitrarily defined as the very begining of the Terran year 1972 according to TAI, minus 31536000 seconds (two non-leap years without leap seconds). The subtraction avoids the issue of leap seconds before 1972; there was no international agreement before then and seemingly no records of such leap seconds are available online. The definition is close to a very common definition of time zero (1970 UTC is more commonly used), and it allows POSIX time to be seen as though it were TAI (no leap seconds) for a direct conversion to Interstellar Time. A proper conversion must add leap seconds to the POSIX time.

In ordered to be at least somewhat worthy of the name Interstellar Time, I decided the primary computer storage form ought to be large enough to last past the Stelliferous Era. It must also be an integer to avoid loss of precision over time. I decided on using a 128-bit integer that stores Interstellar Time in femtoseconds for plenty of resolution. It should last into the begining of the Degenerate Era. Other storage forms are also available that use less memory, but have more limited ranges and less resolution.

Time Intervals in Seconds by Powers of Ten (mostly)

I found this useful while contemplating Human readable formats for Interstellar Time.

Unit	Abrev	Seconds	Similar-ish	Earth Time Equivalent
second	s	1	second	1 second
decasecond	ds	10	tens of seconds	10 seconds
hectosecond	hs	100	minute	1 minute, 40 seconds
kilosecond	ks	1000	quarter hour	16 minutes, 40 seconds
myriasecond	mas	10000	hours	2 hours, 46 minutes, 40 seconds
1e5 seconds		100000	day	1 day, 3 hours, 46 minutes, 40 seconds
megasecond	Ms	1e6	week	11 days, 13 hours, 46 minutes, 40 seconds
1e7 seconds		1e7	months	115 days, 17 hours, 46 minutes, 40 seconds
1e8 seconds		1e8	years	3 years, 61 days, 16 hours, 19 minutes, 4 seconds
gigasecond	Gs	1e9	decades	31 years, 251 days, 13 hours, 21 minutes, 28 seconds
1e10 seconds		1e10	centuries	316 years, 324 days, 2 hours, 39 minutes, 28 seconds
1e11 seconds		1e11	millennia	3168 years, 319 days, 4 hours, 1 minute, 4 seconds
terasecond	Ts	1e12	tens of millennia	31688 years, 269 days, 17 hours, 37 minutes, 4 seconds
petasecond	Ps	1e15	millions of years	31.688738 million years
exasecond	Es	1e18	billions of years	31.688738 billion years
zettasecond	Zs	1e21	trillions of years	31.688738 trillion years

Details worthy of notice:

The prefix myria has been deprecated since 1960.
The length of a year used in the table is 365.2425 days; it is based on the Gregorian calendar.
The length of a day used in the table is always exactly 86400 seconds.

Human Readable Formats

Metric Format

This format follows the regular metric prefix convention of varying by a factor of 1000.

000G 000M 000k 000s 000m

The letters are the metric prefix abreviations without units, excepct for s, since the units are all seconds. Each section jumps by a rather large amount, so I doubt this will work well for most people. It is implemented by duds::time::interstellar::Metricform.

Hecto Format

This format has fields increasing by a factor of 100 to avoid the large jumps of the metric format.

00:00:00-00:00:00

It is implemented by duds::time::interstellar::Hectoform.