Time will literally stand still tonight – for one whole second - as we experience what astrophysicists call a ‘leap second’ in order to compensate for the slowing of the Earth’s rotation.
This year the extra second will be added at 00:59:60 on Wednesday, July 1 (BST) to allow the world’s clocks to catch up with the Earth to make sure they are as accurate as possible.
Before the invention of super-accurate atomic clocks, time was based on the Earth’s rotation, one complete turn taking 24 hours.
Now a plethora of time-sensitive systems, including computer programmes and financial markets, rely on the precise ticking of atomic clocks that measure the energy transitions of atoms.
The problem is that due to the moon’s gravity the Earth is slowing down, and not in a regular way.
So every now and then a leap second is added to allow astronomical time to catch up with atomic time.
Leap seconds were first introduced in 1972, by which time atomic clocks and astronomical clocks were already out of kilter by 10 seconds.
That year, scientists had to add 10 seconds to the world’s astronomical clocks in one go. The impact then in the pre-internet age was nothing like as great as it would have been today.
Fears over time change
The last leap second in 2012 temporarily disrupted a number of high-profile websites including Mozilla, Reddit, Gawker, LinkedIn, FourSquare and Yelp.
There are fears the same could happen again, with financial institutions concerned about potential impact on stock markets are also wary of mishaps, particularly in Australia where the leap second will happen at 10am on 1 July.
The potential problems mean there are vocal opponents of introducing the leap second, but scientists say it is essential for research purposes.
Members of the International Telecommunications Union, which sets the world’s clocks, will meet later this year to decide whether to scrap leap seconds completely.
Experts have suggested such a move means we could slip up to three minutes ahead of time by 2100, and about half an hour by 2700.
What will you do with your extra second?
Who decided to use the leap second?
The International Earth Rotation and Reference Systems Service (IERS) based in France monitors the planet’s rotation and tweak time where necessary.
Dr Daniel Gambis, head of the IERS, announced in January that a “positive leap second” will be added to Coordinated Universal Time (UTC) on June 30, the international time standard which regulates clocks around the world.
In January, they sent out what may be one of the greatest bulletins ever, addressed to “authorities responsible for the measurement and distribution of time.”
UTC is based around atomic time, a method of measuring time based on the frequency of vibrations within an atom.