Episode 05

The Modern Calendar and Global Time

Atomic noon

Railway clocks, time zones, Greenwich, UTC, cesium fountains, leap seconds. The planet shares a second that no longer quite belongs to the Earth.

Beats

• The 1884 Prime Meridian Conference.
• UTC versus UT1, and the leap second as a diplomatic object.
• Whether to abolish the leap second.

Terms

UTC

Civil time: atomic seconds, occasionally stepped to track Earth rotation.

SI second

9,192,631,770 periods of cesium-133 radiation.

Discussion

1. If Earth rotation keeps slowing, who should own the definition of the day?
2. What is gained and lost if leap seconds are abolished?