2015 January 18

Leap Second on June 30

Steve Harvey

On June 30 this year we will get an extra second in bed, as the International Earth Rotation and reference System Service (IERS) have decided to add a leap second to the official UTC time.

UTC is normally in tune with Atomic time (which is constant), but the Earth’s rotation is gradually slowing down by around 1.4ms per day per century. Since 1820, the mean solar day has increased from exactly 86,400 seconds to the present value of about 86,400.002 seconds.  Over the course of one year, the difference accumulates to almost one second, and so occasionally the French organisation responsible for official world timekeeping make the decision to tweak the UTC time to match that measured by Earth’s rotation.
These adjustments have been occurring since 1972, and the last additional second was introduced on 1 July 2012, at 0hUTC.

The USA would prefer to get rid of leap seconds as they believe they were causing problems for communication and navigation systems. The UK, however, argued at a conference in Geneva in 2012, that without adjustment, the link between our concept of time and the rising and setting of the Sun would be lost.

Since 1972, we will be the 26th time a leap second has been added to UTC time.

Later this year at the World Radio communication Conference, delegates will attempt to agree upon the future of using leap second.

Steve Harvey was recently appointed as the new Director of the BAA’s Computing Section.