A Brief History of UTC Leap Second

Abstract

Approximately once a year, since 1972, a leap second is introduced into UTC, the world's atomic time scale for civil time, to keep it in phase with the rotation of the Earth. Leap seconds ensure that, on average, the Sun continues to be overhead on the Greenwich meridian at noon to within about 1 s. The question of leap second is being debated since 2000 in different working groups of various international organizations, especially in the ITU-R WP 7A, is whether there still a need for the leap second, with its many technical inconveniences. In these groups overwhelmingly prevails an opinion that it would be better simply to let atomic time run freely and accept that the world's civil time scale will slowly diverge from the rotation of the Earth. The National Institute of Telecommunications in recent years became one of the leaders of this process. This article gives brief history of the current practice of UTC and outlines various solutions.