Then there are many cycles of earth rotation around the sun and on its own axis. (skepticalscience.com)
When the International Earth Rotation Service calls for it, timing labs in all time zones add a leap second just before midnight in Greenwich, England. (discovermagazine.com)
«In 1972 the leap second was considered a step forward,» says astronomer Dennis McCarthy, who runs the Washington - based time directorate for the International Earth Rotation Service. (discovermagazine.com)