Most of the time zones in the world are based on “Coordinated Universal Time” (UTC, international time standard). However, the earth’s rotation is not as regular and minimally smaller than when this standard was defined. For this reason, so-called “leap seconds” are inserted into the UTC scale from time to time. Since the earth’s natural rotation is not perfectly constant, the insertion of leap seconds is done as needed and according to no fixed pattern. Leap seconds are determined in such a case by the International Earth Rotation and Reference Service (IERS). However, the responsible state institution is usually accountable for the official time of a particular country.
While leap seconds pass unnoticed for most people, they can cause problems for many systems that require an exact, uninterrupted flow of time, such as satellite navigation, software, telecommunication, trade, and even space travel.