TimeSystem
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TimeSystem
is an option for time functions that specifies the time system being used to define time.
Details

- Time systems are also known as time standards, time scales or time references.
- The time system indicates the physical process that determines how to measure the advance of time: atomic oscillations, the rotation of the Earth, some other astronomical phenomenon, etc.
- Choosing the appropriate time system is critical for precise time control. Errors of tens of seconds may accumulate over a few decades, or several hours over a few thousand years.
- The choice of time system is independent from the choice of calendar and the choice of time zone.
- Possible values for time systems include:
-
"TAI" atomic time, as measured by atomic clocks "TCB" solar system barycentric coordinate time "TCG" geocentric coordinate time "TDB","ET" solar system barycentric dynamical time, or ephemeris time "TT" terrestrial time, as measured at sea level on the Earth "UTC" coordinated universal time, including leap seconds "UT1" time proportional to the Earth's rotation angle "UT" UTC with leap second smearing over the previous day, or solar UT1 time outside the UTC period (1960 to now) - The default value of TimeSystem is Automatic, which will inherit the time system of an input if given, and otherwise default to "UT".
Examples
open allclose allBasic Examples (3)Summary of the most common use cases
Define an instant in the UTC time system:

https://wolfram.com/xid/0bimqgma-6wlxe9

Convert to atomic time, which is currently 37 leap seconds ahead of UTC:

https://wolfram.com/xid/0bimqgma-mo1lwl

Convert a UTC date into a Julian date in terrestrial time:

https://wolfram.com/xid/0bimqgma-5e8rp0

Compare with a conversion to a Julian date in UTC time:

https://wolfram.com/xid/0bimqgma-edyxu1

The difference on that date was 64.184 seconds:

https://wolfram.com/xid/0bimqgma-1yp22d

These are different instants of time, separated by 37 leap seconds:

https://wolfram.com/xid/0bimqgma-7ohqyf

Scope (3)Survey of the scope of standard use cases
Specify different time systems in a DateObject expression:

https://wolfram.com/xid/0bimqgma-vr456k


https://wolfram.com/xid/0bimqgma-1an7bu


https://wolfram.com/xid/0bimqgma-juof4e


https://wolfram.com/xid/0bimqgma-z9fe2w


https://wolfram.com/xid/0bimqgma-yy95mj


https://wolfram.com/xid/0bimqgma-48p4tn


https://wolfram.com/xid/0bimqgma-3vz6a0


https://wolfram.com/xid/0bimqgma-c8kwbl

Use different time systems in combination with different calendars:

https://wolfram.com/xid/0bimqgma-8p7nlc


https://wolfram.com/xid/0bimqgma-k2ys5m


https://wolfram.com/xid/0bimqgma-lsq6f4


https://wolfram.com/xid/0bimqgma-tyosdb

The "TDB" time system is also known as ephemeris time "ET":

https://wolfram.com/xid/0bimqgma-b404v0

Converting to the "ET" system does not change the numeric date:

https://wolfram.com/xid/0bimqgma-kuhqps

Applications (1)Sample problems that can be solved with this function
Properties & Relations (2)Properties of the function, and connections to other functions
Use the TimeSystem option to specify the time system of a DateObject expression:

https://wolfram.com/xid/0bimqgma-3bnawd

Use TimeSystemConvert to change that date to a different time system representation:

https://wolfram.com/xid/0bimqgma-ngd9v8

UT1 time for a given time zone corresponds to mean solar time at the corresponding central meridian:

https://wolfram.com/xid/0bimqgma-tq5ddh

Neat Examples (1)Surprising or curious use cases
Between 1960 and 1972, "UTC" frequently added fractional seconds and was more closely aligned to "UT1":

https://wolfram.com/xid/0bimqgma-laiil9

Starting in 1972, "UTC" adds only whole leap seconds, as needed, to remain within 1 second of "UT1":

https://wolfram.com/xid/0bimqgma-bt7qm0

The difference between "TAI" and "UTC" shows the number of leap seconds added since "UTC" began:

https://wolfram.com/xid/0bimqgma-5i0dya

Wolfram Research (2021), TimeSystem, Wolfram Language function, https://reference.wolfram.com/language/ref/TimeSystem.html.
Text
Wolfram Research (2021), TimeSystem, Wolfram Language function, https://reference.wolfram.com/language/ref/TimeSystem.html.
Wolfram Research (2021), TimeSystem, Wolfram Language function, https://reference.wolfram.com/language/ref/TimeSystem.html.
CMS
Wolfram Language. 2021. "TimeSystem." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/TimeSystem.html.
Wolfram Language. 2021. "TimeSystem." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/TimeSystem.html.
APA
Wolfram Language. (2021). TimeSystem. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/TimeSystem.html
Wolfram Language. (2021). TimeSystem. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/TimeSystem.html
BibTeX
@misc{reference.wolfram_2025_timesystem, author="Wolfram Research", title="{TimeSystem}", year="2021", howpublished="\url{https://reference.wolfram.com/language/ref/TimeSystem.html}", note=[Accessed: 08-July-2025
]}
BibLaTeX
@online{reference.wolfram_2025_timesystem, organization={Wolfram Research}, title={TimeSystem}, year={2021}, url={https://reference.wolfram.com/language/ref/TimeSystem.html}, note=[Accessed: 08-July-2025
]}