Blink and you'll miss it - the leap second

Blink and you'll miss it - the leap second

Something special is going to happen tonight that is quite rare and most people won't even notice. We're getting an extra second. Today the 30th June will be twenty four hours and one second long and 23:59:60 will be a real time.

Leap Years

You've all heard of leap years, every fourth year we have an extra day, the 29th Feb. We need it because a year is actually 365.25 days long. What a lot of people don't realise is that just as the year isn't exactly 365 days long, a day isn't exactly 24 hours long either. The variance is much smaller, and it's not constant, but if it was left unchecked, eventually our clocks would lose their relationship to our physical days. For the vast majority of human history, this made no difference whatsoever. It's only in the last 50 years or so, with the rise of super accurate atomic clocks, that it's become an issue.

Leap Seconds

We handle this variation by adding (or in theory subtracting) an extra second into specific days. These seconds are called Leap Seconds ( They are always added to the 30th June or the 31st December at midnight. However, just to keep you on your toes, they are not added on a regular basis, just when they are needed. So far there have been 25, tonight's will be the 26th.

The only downside to Leap Seconds is our dependence on modern computer systems and communications systems. A lot of these are very time sensitive. It is possible for computer to decide to ignore an email sent on June 30th 23:59:60, because it knows that such a time doesn't exist ... well, normally it doesn't exist anyway :-). It could affect finance, computer systems, email and even GPS navigation.

Technological Armageddon?

So will we see a technological meltdown of all our wonderful toys at midnight tonight?

Short answer - no

We might see the odd glitch, some older GPS receivers might report the wrong date for the second at midnight, and it's possible that all the NTP servers on the Internet will take a day or so to get themselves back into sync ... but the normality of life will continue tomorrow and your phones and gizmos will all be working.

Just one second later than normal :-)

So enjoy your extra second tonight however you choose to spend it, either partying, sleeping or whatever :-)

"There's a fine line between genius and insanity. I have erased that line." - Oscar Levant

Header image copyright: