GeoOrientationData
GeoOrientationData[date,prop]
gives the value of the property prop about the orientation of the Earth on the given date.
GeoOrientationData[date,prop,"variant"]
gives the specified variant of the property prop on the given date.
Details
 GeoOrientationData gives information about the orientation of the Earth with respect to the celestial reference frame.
 GeoOrientationData is typically used in applications such as pointing a telescope, monitoring the rotation and wobble of the Earth, or investigating how Earth's rotation has slowed down in the past.
 The gravitational pull of other celestial bodies, the internal motion of mass in the Earth, ocean tides and other physical phenomena modify the average rotation of the Earth and the direction of its rotation axis in unpredictable ways. The consequences of many of those effects are tracked in GeoOrientationData.
 In GeoOrientationData[date,…], date specifications are DateObject or DateInterval expressions representing dates or intervals in the UTC time system.
 Temporal properties describing the inhomogeneous duration of the day include:

"DayDuration" duration in seconds of the day of the given date "DayDurationExcess" excess of the duration of the day over 86400 seconds "LeapSecondCount" number of leap seconds inserted until the given date "LeapSeconds" list of leap seconds added during a given period "TAIMinusUT1" difference between TAI and UT1 times "TAIMinusUTC" difference between TAI and UTC times "UT1MinusUTC" difference between UT1 and UTC times  Properties describing the orientation of the Earth with respect to the terrestrial reference frame include:

"PolarMotion" components of the rotation axis in the ITRF frame "PolarMotionX" component of rotation axis, positive toward Greenwich "PolarMotionY" component of rotation axis, positive toward 90° west "PolarMotionGeoPosition" geodetic location of the instantaneous rotation axis  Properties describing the orientation of the Earth with respect to the celestial reference frame include:

"BiasMatrix" rotation matrix from the ICRF frame to the mean equatorial frame of J2000 "PrecessionMatrix" rotation matrix from the mean equatorial frame of J2000 to the mean equatorial frame of date "NutationMatrix" rotation matrix from the mean equatorial frame of date to the true equatorial frame of date "Obliquity" obliquity angle between the equatorial and ecliptic planes  In GeoOrientationData[date,prop,"variant"] possible variants include:

"Value" value of the property, a number, quantity or geo position "Uncertainty" uncertainty of the measured value, if available "Around" Around[value,uncertainty] object  For dates after 1960 until April 2021, measured data was obtained from the International Earth Rotation and Reference Systems Service (IERS), as well as predicted data from May 2021 to April 2022. Data before 1960 was obtained from the analysis of older astronomical sources, in particular, ancient observation of eclipses. Future data is extrapolated.
Examples
open allclose allBasic Examples (3)
Get the difference between TAI and UT1 times at the beginning of January 1, 2000:
This number of leap seconds had been inserted by then to approximate that result:
Find the observed duration of July 19, 2020:
The excess over 86400 seconds is negative, so this day was shorter than the standard civil day:
Report the result with its uncertainty:
Find the geodetic location of the instantaneous rotational axis of the Earth for a given date:
Scope (5)
Specify dates as DateObject expressions:
Get property values for a list of dates:
Get a time series of property values for a DateInterval input:
Obtain the list of 27 leap seconds introduced since 1972:
There were no leap seconds added in the year 2020:
Obliquity angle between the mean equatorial and the ecliptic planes:
Display the evolution of the obliquity angle for Julian years to :
Applications (4)
Find the excess in day durations for all days since January 1, 1962:
It has changed a few milliseconds in the last few decades:
Recently, the day has been getting shorter:
Show the behavior in the last few years:
Show the behavior in the last few months:
Find the difference between TAI and UT1 for the first day of each month since 1960:
Also get the difference between TAI and UTC, which was piecewise linear from 1960 to 1973 and is now piecewise constant:
UTC follows UT1 in such a way that their difference is never larger than 0.9 seconds:
Locate the instantaneous rotation axis with respect to the geodetic North Pole between 2010 and 2015:
The result is given as a list of pairs of the and components of the rotation axis, usually given as small angles with respect to the North Pole:
The standard convention makes the axis point toward Greenwich on the left and the axis toward 90 degrees west on the top:
Convert to a representation in meters:
Average the polar motion of the instantaneous rotation axis around the geodetic North Pole:
Properties & Relations (3)
Text
Wolfram Research (2021), GeoOrientationData, Wolfram Language function, https://reference.wolfram.com/language/ref/GeoOrientationData.html.
CMS
Wolfram Language. 2021. "GeoOrientationData." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/GeoOrientationData.html.
APA
Wolfram Language. (2021). GeoOrientationData. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/GeoOrientationData.html