When you're counting down to the new year, remember to add 1 second.
Why? Because of waves (more on that below).
The international organizations that make sure our concept of time is more or less the "actual" time decided 2016 needs to be just a little bit longer. Bummer for everyone who wants to get this year over with.
So, a "leap second" will be added when the UTC time strikes midnight – that's just before 6 p.m. in Minnesota. The time will go like this:
Dec. 31, 2016: 23 hours, 59 minutes and 59 seconds.
Dec. 31, 2016: 23 hours, 59 minutes and 60 seconds. (Whoa.)
Jan. 1, 2017: 0 hours, 0 minutes and 0 seconds.
This whole leap second thing is kind of confusing. You can read all the science behind it in this news release from the U.S. Naval Observatory, but we'll break it down for you:
Time is based on the Earth's rotation.
But the Earth's rotation isn't exactly accurate. It's actually slowing down because of ocean tides – waves (which are mainly caused by the tug-of-war between the Earth and moon) act like a brake on the spinning Earth, EarthSky says.
It sounds kind of drastic, but waves don't slow down the Earth that much. A day is said to be 86,400 seconds, but it has actually been 86,400.002 seconds long since about 1820, NASA said.
Even though two milliseconds a day isn't noticeable, it is cumulative. After roughly 500 days, those extra milliseconds add up to about 1 second.
The problem arises when you try to compare the Earth's rotational time to our clocks. The atomic clock is just too accurate, and doesn't account for the slowing Earth that's making our days a teensy, tiny bit longer.
That's where the leap second comes in. The global timekeepers came up with it in the 1970s to keep everything in sync. The Washington Post explains that adding this leap second every year and a half makes it so the atomic clocks don't vary more than 0.9 seconds from the Earth's actual rotational time.
This will be the 27th leap second that's been added; the most recent extra second came on June 30, 2015, EarthSky says. Note: Leap seconds are always added either at the end of June or the end of December.
Want some ideas on how to spend your extra second Saturday night? Back in 2015, John Oliver gave some ideas on Last Week Tonight: