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General Information About Earth orientation

IERS Conventions 2010

The Conventions contains detailed information on definitions and models used to determine Earth Orientation.
Refer here for the latest updates to the Conventions.

IERS Conventions 2003

Please note: This links to the 2003 IERS Conventions.

IERS Conventions 1996

Please note: This links to the 1996 IERS Conventions.

Units commonly used for Earth Orientation

1 mas = 1 milliarcsecond = 1 thousandth of a second of arc (for polar motion & nutation);
1 ms = 1 millisecond = 1 thousandth of a second of time (for UT1);
1 mas equals an equatorial shift at the Earth's surface of 3.1 cm;
1 ms equals the time it takes for the Earth to spin 15 mas (46.5 cm at the equator)

Date and Time Definitions

Date Definitions:
Modified Julian Date (MJD):
MJD = Julian Date - 2,400,000.5 days
T, the Besselian date, is given by T = 2000.000 + (MJD - 51544.03) / 365.2422
Time Definitions:
UT2-UT1 = 0.022 sin(2*pi*T) - 0.012 cos(2*pi*T) - 0.006 sin(4*pi*T) + 0.007 cos(4*pi*T)
where pi = π and T is the date in Besselian years.
  • TT = TAI + 32.184 seconds
  • since 00h 00m UTC 01 Jan 2017, the cumulative leap second count is:
    TAI-UTC = 37 seconds (exactly)
    and GPS Time-UTC = 18 seconds
  • users may compute Delta T = TT - UT1 using the relation:
         Delta T = 32.184 s + (TAI - UTC) - (UT1 - UTC)
         (TAI - UTC) is the cumulative number of leap seconds
         (UT1 - UTC) is a standard Earth Orientation product.


Interpolating IERS Earth Orientation data

This is the IERS Gazette #13 (ASCII).  Please note that the recommended routine does not interpolate UT1-UTC properly around a leap second.

Data series used in IERS Bulletin A

These are the raw observations which contribute to IERS Bulletin A.

Systematic Corrections

Systematic corrections that are applied to Combination procedure.

Changes to Bulletin A (archive)

Archive of changes to Bulletin A since 2007.

Past issues of Bulletin A

Past issues of Bulletin A are archived at Crustal Dynamics Data Information Center (CDDIS).

Plots of Past Earth Orientation

Plots of past EOP variations (including comparisons with atmospheric excitation).

Bulletin B

Bulletin C

IERS Bulletin C announces leap seconds.  To learn what a leap second is, refer to the FAQ.

Bulletin D

IERS Bulletin D announces UT1-UTC values.
  • values of DUT1 = (UT1-UTC) transmitted with time signals are published in IERS Bulletin D to a precision of 0.1 s
  • previous issues of Bulletin D are archived here.  |  |  Navy FOIA  |  DoD Accessibility/Section 508  |  No Fear Act  |  Open Government  |  Plain Writing Act  |  Veterans Crisis Line  |  DoD Safe Helpline  |  Navy SAPR  |  NCIS Tips  |  Privacy Policy  |  Contact Webmaster
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