Leap second: Why tomorrow will be longer than today

CHICAGO (WLS) -- Something unusual will happen on the night of Tuesday, June 30. The world gets an extra second, or a "leap second"!

The extra second comes in that final minute before the clock strikes 7 p.m. CT. Instead of 60 seconds, that minute will be 61 seconds long.

Leap seconds aren't new. They are scheduled occasionally to keep atomic clocks in sync.

The "leap second" was unleashed in the 1970s as a way to make up for slight variations in time. Basically, the earth doesn't rotate at exactly the same rate every year so this small adjustment allegedly keeps us all on track.

But this year's leap second coincides with the opening of many Asian financial markets, so extra-second-worries have set in.

The NASDAQ is shutting down at 7:48 p.m. Eastern. Other major exchanges are also trading early or opening late.

There is reason for concern. In 2012, a leap second crashed multiple sites, including Yelp, Reddit and Foursquare. Qantas Airlines lost their entire system for hours -- checking in passengers by hand.

Google has a fix in place. The company will add milliseconds to its servers all day instead of one whopping second all at once.