The Leap Second Debate and the Lessons from Timekeeping History

Abstract

Timekeeping, together with navigation, is one of the oldest missions of astronomy, originating long before the dawn of written history. The ancient and sacred task of timekeeping, linking the eternal with the everyday, stood at the origin of the Vatican Observatory. The history of timekeeping schemes throughout millennia has been a search for a balance between the practical and the symbolic. The current debate focuses on the Leap Second, a mechanism first applied in 1972. Atomic clocks, careful observations of distant quasars, etc. tell us that the Earth spins somewhat irregularly. The symbolic value of coupling civil timekeeping to the heavens is so strong, however, that the international community still requires the International Telecommunication Union to broadcast time signals following Earth’s rotation. In order to reconcile this symbolically significant requirement with the practicality of uniformly flowing atomic time, a leap second is added (or subtracted) from the otherwise perfectly regular sequence, so that every so often there is a minute with 61 (or 59) seconds. This system is currently under review, with a proposal on the table to abandon the leap second, decoupling civil timekeeping from astronomical phenomena. Social mechanisms involved in timekeeping can be studied by examining the historical evidence related to calenders. These lessons may provide a broader context for the leap-second debate and they may shed light on it. Calculated timekeeping does not actually agree with the heavens at any given moment, but this does not seem to jeopardize the general perception of its astronomical conformity since it is rightly perceived as a way of preserving it on average. The current proposal, however, clearly entails decoupling civil time from Earths rotation. If presented as a definitive solution, it would result in a direct and unprecedented breach with the principle of astronomical conformity. If presented as a temporary measure, to be applied until a better solution is found, it would preserve the principle of astronomical conformity because the latter fulfills its social function even when it is not observed perfectly considering that in the realm of symbolism what counts is the general perception, not the fact.