Clock vault at the U.S. Naval Observatory in Washington

Timekeepers are planning to delay the start of the New Year for an instant later this week, when they add one second to official clocks.

The U.S. Naval Observatory in Washington, which is part of an international agreement that sets Coordinated Universal Time or UTC, says the addition of a so-called "leap second" is needed to syncronize official atomic clocks with the earth's rotation.

While the earth's rotation makes for a nearly perfect 24-hour day, atomic clocks measure time based on properties of atoms.

The last leap second was added to the world's clocks in 1998.