Oh, you think today, June 21, 2015, is the longest day of 2015?
Sorry, Summer Solstice. This year, June 30 wins by one second.
2015 is a leap second year, when an extra second is added to the Coordinated Universal Time (UTC). So June 30, 2015 will have 86,401 seconds instead of the 86,400 seconds to which we’ve become accustomed.
Better start planning now to make sure you take full advantage of that extra time.
Why am I writing about this? I finally have a good reason to try a countdown widget, which is set for 23:59:60 on June 30, 2015 UTC (or 18:59:60 Chicago) when the extra second will be inserted.
An extra second? Seriously?
Apparently, it is a very serious bookkeeping issue. Official time is kept with utmost precision by an atomic clock. Unfortunately, the Earth is not so precise. Our planet dutifully spins round and round, day after day. But it gets slowed down on occassion by the braking action caused by tides. (When you think about all that water sloshing across our blue planet, it’s a wonder more things don’t go off kilter.) Hence, the International Earth Rotation and Reference Service (IERS) adds a second every few years to reconcile the precision of the atomic clock with what’s actually happening with Earth rotation. More information: U.S. Naval Observatory.
Not quite Y2K, but still messy
This extra second can really screw up computer systems. Remember that extra second added back in 2012? LinkedIn, Qantas Airways, Yelp and Reddit do. Although added over a weekend, these websites and several others had issues.
This time, Chicago Mercantile Exchange and several other trading systems are delaying start of trading until that extra second passes. When millions of dollars can be traded in mere nanoseconds, a lot can go wrong in that extra second.