  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 Earth's 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, it's important to
understand the history of human timekeeping.
