… well, longer by 1 second that is. A leap second will be added on Saturday 30 June 2012 at 23:59:60 UTC (Coordinated Universal Time).

Leap seconds are occasionally inserted to keep UTC close to the mean solar time. By tradition, our clock time is related to the position of the Sun in the sky, which is in turn determined by the rotation of the Earth. But the Earth’s rotation rate is slightly variable, depending on factors like tidal friction and other processes which cause major mass redistribution. So Coordinated Universal Time (UTC) has been defined in order to keep the apparent position of the Sun in the sky, and hence our concept of the day, in line with International Atomic Time (TAI).

UTC is defined as being an integral number of seconds different from TAI so as to keep the Earth’s rotation linked with the day. This number of seconds is altered by one each time that the Earth’s irregular rotation has produced a difference amounting to a second.

These leap seconds are added (or subtracted) at either the end of the year (31 December) or halfway through the year (30 June).

The most recent leap second was added on 31 December 2008, and the one prior to that was on 31 December 2005.

The summer solstice occurs today, 20 June 2012, at 23.09 UTC (GMT).

The summer and winter solstices mark the times when the Sun is at its furthest from the celestial equator (the projection of the Earth’s equator onto the sky) – or in other words, when the Sun reaches its highest position in the sky (as seen from the North pole for the summer solstice). Unless you happen to live in polar regions, the summer solstice is also the day with the longest daylight.

The world solstice comes from the Latin solstitium meaning ‘Sun stands still’ because the apparent movement of the Sun’s path north or south stops before changing direction.

The summer solstice usually falls on 21 June, but not always. Because the Earth takes approximately 365.25 days to go around the Sun, the precise time of the solstices occurs about 6 hours later each year, with a jump of a day backwards on leap years (such as 2012).

Find out more about solstices and equinoxes in our fact file. And enjoy the long daylight hours!