Hopefully your Tuesday is off to a great start because there's going to be just a little bit more of it than we're used to. Our very precise modern clocks measure exactly 86,400 seconds between one midnight and the next. Unfortunately, one full rotation of the Earth actually takes 86,400.002 seconds because of the way the oceans work against the gravitational forces of the various celestial bodies to ever so slightly slow the Earth's spin. To accommodate this, all those milliseconds are lumped together into a full second that is added to the year at a predetermined to time to re-sync our clocks with the Earth's rotation. Today is that time. The extra second is added at the very end of the day, 11:59 p.m., according to Coordinated Universal Time (UTC). Here in New York, and the rest of the East Coast, that will translate to 7:59 p.m.
This year features the 25th such leap second to be added since scientists at the International Earth Rotation and Reference Systems Service first started calling for them in 1972. These days, though, they're being added at a slower rate because the Earth's rotation is slowing more gradually than it was in the '70s. Of course, the earth's rotation was variable even before then, but modern technologies like satellite navigation require a level of precision that makes such adjustments necessary.
Or at least that's how the International Earth Rotation and Reference Systems Service and some countries feel. Others, including the United States, think adding the seconds is a cumbersome process, especially considering the scale of inaccuracy. If leap seconds were done away with, it's estimated that it would take over 200 years for our bodies to register even an hour difference in the way the clocks reflect the time of day.
Opponents cite the billions of devices around the world that rely on absolute precision that could suffer Y2K style bugs later today. Computer systems, especially those that live on the Internet, might not be prepared to handle an extra second, especially because there were no leap seconds added between 1999 and 2002 while the web was in its formative stages. When the last leap second was added in 2012, sites as big as Amazon and Reddit faced associated issues. This year, Amazon and others like Google, have instituted various ways to account for the extra second, adding it at the end of 11:59 p.m. or divvying it up into even tinier segments of time throughout the day.
But the opposition will have to wait for another year to mount their case against the leap second. For now, start thinking about how you can best use the extra time today.