Midnight came later on Tuesday June 30 as one extra second was added to clocks around the world.
This so-called “leap second” means the last minute of June had 61 seconds in it. Just like leap years, leap seconds are added as a basic way to keep the clock in sync with the Earth and its seasons.
The Paris-based International Earth Rotation and Reference Systems Service charged with ensuring that Earth time keeps pace with time measured by atomic clocks ruled that a tiny pause was needed to account for a gradual slowing-down in the earth’s rotation.
“The Earth’s rotation is unreliable, frivolous, it’s not regular, it varies, so much so that from time to time we need to set the clocks to the right time, and as we can’t change the earth rotation – you’d have to turn it – we change the Coordinated Universal Time (UTC) by adding a leap second,” says Daniel Gambis, astronomer and head of the International Earth Rotation and Reference Systems Service.
The trouble is that the world’s computers aren’t always prepared to accommodate this extra second. Following the last leap second in 2012, web services such as Reddit went dark, as did machines at Qanta Airways, causing flight delays in Australia.
“Nowadays there are more and more networks, telecommunication systems, the internet, etc. that use increasingly automated systems which rely on precise synchronization and dating,” explains Sebastien Bize, joint director of the Observatory’s Space Time Reference Systems. “And it’s for those systems that this unusual operation of a leap second can potentially be a problem.”