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Register a new userThe Future of Time: UTC and the Leap Second
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Before atomic timekeeping, clocks were set to the skies. But starting in 1972, radio signals began broadcasting atomic seconds and leap seconds have occasionally been added to that stream of atomic seconds to keep the signals synchronized with the actual rotation of Earth. Such adjustments were considered necessary because Earths rotation is less regular than atomic timekeeping. In January 2012, a United Nations-affiliated organization could permanently break this link by redefining Coordinated Universal Time. To understand the importance of this potential change, its important to understand the history of human timekeeping.
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We examine the possibility to extend leap second extrapolation for a near future based on some periodic terms in the Earths rotation changes. The IERS data, covering the interval from 1962.15 to 2006.95, are analyzed. The difference $Delta T$ is extrapolated till to 2035 and compared with the IERS extrapolated values to the 2012. It can be seen that for the interval from 2006 to 2024 only 1 leap seconds (negative) will be operated.
The Long Now Foundation is building a mechanical clock that is designed to keep time for the next 10,000 years. The clock maintains its long-term accuracy by synchronizing to the Sun. The 10,000-Year Clock keeps track of five different types of time: Pendulum Time, Uncorrected Solar Time, Corrected Solar Time, Displayed Solar Time and Orrery Time. Pendulum Time is generated from the mechanical pendulum and adjusted according to the equation of time to produce Uncorrected Solar Time, which is in turn mechanically corrected by the Sun to create Corrected Solar Time. Displayed Solar Time advances each time the clock is wound, at which point it catches up with Corrected Solar Time. The clock uses Displayed Solar Time to compute various time indicators to be displayed, including the positions of the Sun, and Gregorian calendar date. Orrery Time is a better approximation of Dynamical Time, used to compute positions of the Moon, planets and stars and the phase of the Moon. This paper describes how the clock reckons time over the 10,000-year design lifetime, in particular how it reconciles the approximate Dynamical Time generated by its mechanical pendulum with the unpredictable rotation of the Earth.
Unless we change direction, we are likely to wind up where we are headed. (Ancient Chinese proverb)
This article is a commentary on the verdict of the LAquila Six, the group of bureaucrats and scientists tried by an Italian court as a result of their public statements in advance of the quake of 2009 Apr. 6 that left the city in ruins and cause more than 300 deaths. It was not the worst such catastrophic event in recent Italian history, but it was one of -- if not the -- worst failures of risk assessment and preventive action. The six were found guilty and condemned by a first level of the justice system to substantial prison terms. The outcry provoked by the verdict in the world press and the international scientific community has fueled the already fiery debate over whether the six should have been tried at all. They have been presented as martyrs to science being treated as scapegoats by a scientifically illiterate justice system and inflamed local population for not being able to perform the impossible (predict the event). Petitions of support have been drafted and signed by thousands of working scientists and technical experts in many fields excoriating the court and the country for such an outrage against the scientific community, often accompanied by ominous warnings about the chilling effect this will have on the availability of expert advice in times of need. My purpose in this essay is to explain why this view of the events of the trial is misguided, however well intentioned, and misinformed.
The European Pulsar Timing Array (EPTA) is a multi-institutional, multi-telescope collaboration, with the goal of using high-precision pulsar timing to directly detect gravitational waves. In this article we discuss the EPTA member telescopes, current achieved timing precision, and near-future goals. We report a preliminary upper limit to the amplitude of a gravitational wave background. We also discuss the Large European Array for Pulsars, in which the five major European telescopes involved in pulsar timing will be combined to provide a coherent array that will give similar sensitivity to the Arecibo radio telescope, and larger sky coverage.
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