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TimeSystem
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TimeSystem

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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 all

Basic Examples  (3)Summary of the most common use cases

Define an instant in the UTC time system:

In[1]:=1
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https://wolfram.com/xid/0bimqgma-6wlxe9
Out[1]=1

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

In[2]:=2
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https://wolfram.com/xid/0bimqgma-mo1lwl
Out[2]=2

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

In[1]:=1
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https://wolfram.com/xid/0bimqgma-5e8rp0
Out[1]=1

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

In[2]:=2
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https://wolfram.com/xid/0bimqgma-edyxu1
Out[2]=2

The difference on that date was 64.184 seconds:

In[3]:=3
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https://wolfram.com/xid/0bimqgma-1yp22d
Out[3]=3

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

In[1]:=1
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https://wolfram.com/xid/0bimqgma-7ohqyf
Out[1]=1

Scope  (3)Survey of the scope of standard use cases

Specify different time systems in a DateObject expression:

In[1]:=1
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https://wolfram.com/xid/0bimqgma-vr456k
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0bimqgma-1an7bu
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0bimqgma-juof4e
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0bimqgma-z9fe2w
Out[4]=4
In[5]:=5
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https://wolfram.com/xid/0bimqgma-yy95mj
Out[5]=5
In[6]:=6
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https://wolfram.com/xid/0bimqgma-48p4tn
Out[6]=6
In[7]:=7
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https://wolfram.com/xid/0bimqgma-3vz6a0
Out[7]=7
In[8]:=8
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https://wolfram.com/xid/0bimqgma-c8kwbl
Out[8]=8

Use different time systems in combination with different calendars:

In[1]:=1
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https://wolfram.com/xid/0bimqgma-8p7nlc
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0bimqgma-k2ys5m
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0bimqgma-lsq6f4
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0bimqgma-tyosdb
Out[4]=4

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

In[1]:=1
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https://wolfram.com/xid/0bimqgma-b404v0
Out[1]=1

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

In[2]:=2
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https://wolfram.com/xid/0bimqgma-kuhqps
Out[2]=2

Applications  (1)Sample problems that can be solved with this function

Explore the transition during the last added leap second, at the end of year 2016:

In[1]:=1
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https://wolfram.com/xid/0bimqgma-xgzdm
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0bimqgma-ek1luq
Out[2]=2

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:

In[1]:=1
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https://wolfram.com/xid/0bimqgma-3bnawd
Out[1]=1

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

In[2]:=2
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https://wolfram.com/xid/0bimqgma-ngd9v8
Out[2]=2

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

In[1]:=1
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https://wolfram.com/xid/0bimqgma-tq5ddh
Out[1]=1

Neat Examples  (1)Surprising or curious use cases

Between 1960 and 1972, "UTC" frequently added fractional seconds and was more closely aligned to "UT1":

In[1]:=1
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https://wolfram.com/xid/0bimqgma-laiil9
Out[1]=1

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

In[2]:=2
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https://wolfram.com/xid/0bimqgma-bt7qm0
Out[2]=2

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

In[3]:=3
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https://wolfram.com/xid/0bimqgma-5i0dya
Out[3]=3
Wolfram Research (2021), TimeSystem, Wolfram Language function, https://reference.wolfram.com/language/ref/TimeSystem.html.
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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.

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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.

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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

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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 ]}

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@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 ]}

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@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 ]}