International Earth Rotation and Reference Systems Service Service International de la Rotation de la Terre et des Systemes de Reference

The IERS Rapid Service/Prediction Center is the product center of the International Earth Rotation and Reference Systems Service responsible for providing Earth orientation parameters (EOPs) on a rapid turnaround basis. This service is primarily intended for real-time users and others needing the highest quality EOP information sooner than is available in the IERS final series (Bulletin B) published by the IERS Earth Orientation Center, which is based at the Observatoire de Paris.

This Center is an activity of the Earth Orientation (EO) Department at the U.S. Naval Observatory (USNO). The mission of the USNO includes determining the positions and motions of celestial bodies, measuring the Earth's rotation and orientation, maintaining the master clock for the U.S., and disseminating precise time (atomic and astronomical). The EO Dept. contributes to this mission by collecting suitable observations and performing data analyses to determine and predict the time-varying orientation of the terrestrial reference frame within the quasi-inertial celestial reference frame. The key parameters determined and disseminated are polar motion coordinates, Universal Time (UT1), precession, and nutation. The user community is very broadly based, the main applications involving principally high-accuracy navigation and positioning, particularly in real-time and near real-time modes. Contact Information: 202-762-0242 (primary); 202-762-1444 (alternate)

 2009 IERS Bulletin A Vol. XXII Website  

General Information about Earth Orientation

• FAQ: What is Earth orientation?
• refer to IERS Conventions (2003) for detailed information on definitions and models
• refer to the Naval Observatory Vector Astrometry Subroutines (NOVAS) package for software to compute a variety of astrometric quantities and transformations (including terrestrial <---> celestial).
• plots of past EOP variations (including comparisons with atmospheric excitation)
• 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)
• Modified Julian Date (MJD):
  MJD = Julian Date - 2,400,000.5 days
• 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 = 3.14159265... and T is the date in Besselian years.
• T, the Besselian date, is given by T = 2000.000 + (MJD - 51544.03) / 365.2422
• TT = TAI + 32.184 seconds
• since 00h 00m UTC 01 January 2009, the cumulative leap second count is:
  TAI-UTC = 34 seconds (exactly)
  and GPS Time-UTC = 15 seconds
  
• users may compute Delta T using the relation:
       Delta T = 32.184 s + (TAI - UTC) - (UT1 - UTC)
  where
       (TAI - UTC) is the cumulative number of leap seconds
  and
       (UT1 - UTC) is a standard EOP product available below.
  

  NO positive leap second will be introduced at the end of December 2009.
  The last leap second was positive and was introduced in UTC at the end of December 2008.
  (see IERS Bulletin C 38)

IERS Bulletin A -- Rapid Service/Prediction of Earth Orientation

IERS Bulletin A reports the latest determinations for polar motion, UT1-UTC, and nutation offsets at daily intervals based on a combination of contributed analysis results using data from Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Positioning System (GPS) satellites, and Lunar Laser Ranging (LLR). Predictions for variations a year into the future are also provided. Meteorological predictions of variations in Atmospheric Angular Momentum (AAM) are used to aid in the prediction of near-term UT1-UTC changes. This publication is prepared by the IERS Rapid Service/Prediction Center.
• latest issue of IERS Bulletin A -- currently updated weekly (Thursday);
  the contents are described here; to subscribe use the Request Form.
• Prediction coefficients only.

  Additional information concerning IERS Bulletin A:

• explanatory supplement to IERS Bulletins A and B
• interpolating IERS Earth orientation data (IERS Gazette #13)
• input data series used in IERS Bulletin A
• systematic corrections applied to input data series
• plots of Bulletin A combination and residuals
• statistical report for contributed series
• archive of changes to Bulletin A
• past issues of Bulletin A are archived at CDDIS

  Publications about IERS Bulletin A:

• Product Centre report for IERS Annual Report 2002 (pdf format)
• Complete version of IERS Annual Report 2002 (web link to pdf format files)

  Standard data files available by anonymous ftp -- now updated weekly (Thursday), prior to 1 July 2002 (Tuesday and Thursday):

• finals.all -- all EOP values since 02 January 1973 (with 1 year of predictions)
• finals2000A.all -- all EOP values since 02 January 1973 with dX & dY using IAU2000A Nutation/Precession Theory (with 1 year of predic tions)
• finals.data -- same as "finals.all" except since 01 January 1992
• finals2000A.data -- polar motion, UT1-UTC, and length of day since 01 January 1992 with dX & dY using IAU2000A Nutation/Precession Theory (with 1 year of predictions)
• readme.finals -- format for "finals.all" and "finals.data"
• readme.finals2000A -- format for "finals2000A.all" and "finals2000A.data"
• gpsrapid.out -- all EOP values since 01 May 1992 (with 15 days of predictions)
• readme.gpsrapid -- format for "gpsrapid.out"
• mark3.out -- polar motion and UT1-UTC in simple tabular format (with 90-day predictions)
• search the Bulletin A EOP Database

  Daily data files available by anonymous ftp -- updated daily (normally about 17:05 UTC), for highest accuracy real-time applications

• finals.daily -- all EOP values for last 90 days (with 90 days of predictions)
• finals2000A.daily -- polar motion, UT1-UTC, and length of day values for last 90 days with dX & dY using IAU2000A Nutation/Precession Theory (with 90 days of predictions)
• readme.finals -- format for "finals.daily"
• readme.finals2000A -- format for "finals2000A.daily"
• gpsrapid.daily -- all EOP values for last 90 days (with 15 days of predictions)
• readme.gpsrapid -- format for "gpsrapid.daily"

  Delta T values

• Monthly determinations of Delta T -- values of (TT - UT1) since 1973
• Long-term predictions of Delta T -- predictions of (TT - UT1)
• Historic Delta T and LOD -- from McCarthy and Babcock (1986)

  Discontinued data files -- no longer available:

• TPM data file -- low-accuracy EOP prediction coefficients

IERS Bulletin B ("Final" EOP values)

IERS Bulletin B reports the "final" determinations for polar motion, UT1-UTC, and nutation offsets at five-day intervals. Smoothed one-day values are also provided. IERS Bulletin B is prepared by the IERS Earth Orientation Center based at the Paris Observatory and is updated monthly.
• latest issue of IERS Bulletin B -- updated monthly; to subscribe use the Request Form.
• explanatory supplement to IERS Bulletins A and B
• interpolating IERS Earth orientation data (IERS Gazette #13)

IERS Bulletin C (Leap Second Announcements)

• FAQ: What is a leap second?
• information about leap second announcements
• current Leap Second Announcement; to subscribe use the Request Form.
• table of leap seconds since 1961 -- differences between International Atomic Time (TAI) and Coordinated Universal Time (UTC)

IERS Bulletin D (Announcements of DUT1)

• values of DUT1 = (UT1-UTC) transmitted with time signals are published in IERS Bulletin D to a precision of 0.1 s; to subscribe use the Request Form.
• previous issues of Bulletin D are archived here

General Publications

• IERS Annual Report 2002
  
• IERS Annual Report 2001
  
• IERS Annual Report 2000
  
• IERS Conventions (2003), IERS Technical Note 32
  
• IERS Explanatory Supplement -- provides further information about Earth orientation parameters and details about the various services