There are 86,400 seconds in an average day. Except for tomorrow. Tomorrow, there will be 86,401.

You’ve heard of Leap Year? Well, this weekend will be one second longer thanks to the slowing of the earth’s rotation and the need to keep the time of day close to the mean solar time.

Known as a Leap Second, this one second time adjustment will be inserted tomorrow night at one second before midnight, that’s Coordinated Universal Time (UTC).

Leap Seconds occur about every 18 months, scheduled by International Earth Rotation and Reference Systems Service (IERRSS). The scheduling of the additional second comes whenever the UTC gets to .6 seconds off.

Unlike Leap Years, Leap Seconds happen simultaneously around the world at the same time. Leap Seconds usually occur the last day of June or the last day of December, and are announced six months prior to the event, because the Earth’s rotation speed changes irregularly and is quite unpredictable in the long term. But the addition of the one second every year and a half or so is the norm to keep the UTC on track with solar time.

Here in this part of the world, converting to EST, it’s one second before 7 p.m. Saturday night. Got any plans?