Dux Nest

10

9

8

7

6

5

4

3

2

1

+ 1

Happy New Year!

New Year 2009 was a leap second longer than normal. Who decides that we are going to change our clocks?

The International Earth Rotation and Reference Systems Service (IERS) that is who.

Leap seconds, added once every 500 days or so, keep high-precision atomic clocks from running ahead of solar time, which is gradually falling behind as tidal friction slows Earth’s rotation. Michael Schirber.  (2005). U.K. Stargazers: Save the Leap Second. Science, 309(5744), 2147.

Deciding whether and when a leap second is needed falls to an international organisation called the International Earth Rotation and Reference Systems Service (IERS). It collects and averages measurements of the Earth’s rotation from around the world. Each January and July it issues a notice announcing whether a leap second is required in the next six months. James Randerson,  Science correspondent. (2008, December 31). Front: 5, 4, 3, 2, 1 … er 1. New Year to take extra second to reach big bang: Atomic clocks come into line with astronomical day: Erratic rotation of Earth creates need for change. The Guardian,3.

The periodic insertion of a leap second step into the scale of Coordinated Universal Time (UTC) necessitates frequent changes in complex timekeeping systems and is currently the subject of discussion in working groups of various international scientific organizations. UTC is an atomic time scale that agrees in rate with International Atomic Time (TAI), but differs by an integral number of seconds, and is the basis of civil time. In contrast, Universal Time (UT1) is an astronomical time scale defined by the Earth’s rotation and is used in celestial navigation. R A Nelson, D D McCarthy, S Malys, J Levine, B Guinot, H F Fliegel, R L Beard and T R Bartholomew Satellite Eng. Res. Corp., USNO, NIMA, NIST, OP, Aerospace Corp., NRL, Litton TASC Inc.

The International Earth Rotation Service (IERS) was established in 1987 by the International Astronomical Union and the International Union of Geodesy and Geophysics and it began operation on 1 January 1988. It replaced the International Polar Motion Service (IPMS) and the earth-rotation section of the Bureau International de l’Heure (BIH); the activities of BIH on time are continued at Bureau International des Poids et Mesures (BIPM). Since 1 January 2001 the IERS has got a new structure. In 2003 it was renamed to International Earth Rotation and Reference Systems Service.

The definition of UTC was implemented in 1972, principally to accommodate celestial navigation and follows recommendation 460 of the International Radio Consultative Committee (CCIR) in 1970. Since 1972 the use of electronic means to navigate has overtaken celestial navigation. Dennis McCarthy,  F Arias,  W Dick,  D Gambis,  M Hosokawa,  W Klepczynski,  S Leschiutta,  J Laverty,  Z Malkin,  D Matsakis,  R Nelson,  J Vondrak,  P Wallace,  N Capitaine,  T Fukushima. (2005). Division I Working Group on “Definition of Coordinated Universal Time”. International Astronomical Union. Proceedings of the International Astronomical Union, 1(T26A), 63-66.

The leap second has been used sporadically at the Royal Observatory at Greenwich since 1972, an adjustment that has kept Greenwich Mean Time the agreed time standard.

Some scientists now say GMT should be replaced by International Atomic Time - computed outside Paris - because new technologies have allowed atomic time to tick away with down-to-the-nanosecond accuracy.

But opponents say atomic time’s very precision poses a problem. A strict measurement, they say, would change our very notion of time forever, as atomic clocks would one day outpace the familiar cycle of sunrise and sunset.

Atomic time advocates argue that leap seconds are onerous because they’re unpredictable. Since the exact speed of the Earth’s rotation can’t be plotted out in advance, they’re added as needed. Sometimes they’re added Dec. 31; other times at the end of June.

Those fixes can trip up time-sensitive software, particularly in Asia, where the extra second is added in the middle of the day.

Critics say everything from satellite navigation to cellular communication is vulnerable to problems stemming from programs ignoring the extra second or adding it at different times. Raphael G. Satter,  Jamey Keaten Associated Press. (2008, December 31). Wait a sec, 2009; Earth’s running late. Journal - Gazette,A.10.

So what is the time?

Tags: Atomic, Clocks, Earth, Measurement, Rotation, Time, Universal.