Keeping clocks in sync with the sun can be tougher than it seems. Image: Flickr / jorge-11 / CC-BY-SA

Keeping clocks in synch with the way the planet and sun rotate has always been a challenge. While most of us are used to the leap year, governments are set to hash out the question of keeping or getting rid of the leap second.

The idea of a leap second

Since 1972, international time has been coordinated as a part of Coordinated Universal Time (UTC), managed by the International Telecommunications Union. Global positioning systems, computer systems, atomic clocks, and just about everything else technological relies on UTC. About once a year, an additional second is added to the clock in order to keep time in sync with the position of the sun and moon. The ITU’s radio communications assembly, based in Geneva, dictates when these seconds are added.

An argument for no leap second

The wobble between the earth, sun, moon and our land-based clocks is very minor. Britain, China and Canada have all come out in support of the leap second and the idea of keeping clocks as close to in sync with celestial time as possible. The United States and France have both come out against the leap second. The argument is that leap seconds, because the occur on an irregular and unpredictable basis, makes it difficult for programmers and and computer systems not directly connected to atomic clocks to match to exact time. Not making the switch with leap seconds can lead to digital time mismatches that could cost millions of dollars, shut off power grids, or even damage the safety of air traffic control.

What would happen without the leap

If leap seconds were entirely eliminated from the international clock, clocks would slowly get out of sync with solar time. Generally, eliminating leap seconds would pull the clock about a minute and a half out of solar time over 100 years. It would take approximately 9,600 years, but the clock and calendar would eventually be off of solar and celestial time by a full day.


Scientific American

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