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The fractious leap second debate

You might not have heard about it, but there’s a debate going on which threatens to redefine time as we measure it. I’m something of a time nerd; all the computers in our house are synchronized to atomic clocks, as are several of our regular clocks, my wristwatch, and my phone. The debate going on concerns leap seconds. To understand the importance of it, it’s necessary to understand what a leap second is.

Recording time is made difficult for us by the fact that we live on a large rotating object with high mass, in orbit around a star. We like our time measurements to correspond to the apparent observed motion of the star in our sky; in short, we like day to be light, and night to be dark. We also like to set our calendar based on the earth’s orbit around the sun, so that winter is always cold and summer is always hot.

Inconveniently, the earth does not make an exact number of rotations per year. Hence every now and again it’s necessary to have a leap year, inserting an extra day into the calendar to bring it back into sync with the earth’s orbit, so that the months don’t gradually drift against the cycle of hot and cold weather.

The problem of wanting day to be light is solved by having time zones, with different parts of the world choosing a different offset in hours so that noon is roughly when the sun is overhead.

Historically, the offsets were measured from GMT, time as measured at the Greenwich Observatory in England, calculated from the position of the sun. However, the development of atomic clocks of increasing accuracy, and telescopes of increasing power, made scientists aware of problems with this simple scheme.

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