How to talk popular about the leap second? The experience of the IERS Central Bureau

Dick, Wolfgang

During recent years, and especially in 2015, the interest of the public in the leap second has increased considerably. This is mainly due to the discussions about the redefinition of UTC and the claims that the leap second may threaten computer systems. The IERS Central Bureau got a large number of requests from journalists about the leap second, invitations to interviews for radio and TV, and requests for public talks.

Even astronomers and geodesists are often confused about the difference between the slow increase of the Length of Day (LOD) with time on the one hand and the rather large frequency of leap seconds on the other hand. To explain this difference in a popular manner, we use two clocks as a model, of which one is showing exact time, and the other is too slow. This model can then easily be transferred to UTC (exact clock) and UT1 (Earth as clock with LOD > 0).

Another frequently asked question is the future of the time system with and without leap seconds. A table will be presented which shows LOD, Delta T and the time between two leap seconds over the next 2000 years. It can easily be seen that the current system which allows a maximum of 4 leap seconds per year will fail in about 500 years from now, and that Delta T will be about 4 hours in 2000 years from now. This means that the sun would rise only at noon in winter time in the year 4000, if leap seconds would be abolished and current time zones would remain unchanged.

This paper will also summarize the experience of talking about the leap second to journalists and its presentation in mass media.

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