Neil deGrasse Tyson, friendly astrophysicist extraordinaire, has informed us via Facebook that the minute of 4:59 p.m. Pacific Time will have 61 seconds in it.

Why is this happening!? He explains:

Today marks the 26th time a Leap Second will be added to the calendar. In the second half of the 20th century, we started tracking time via atomic clocks, which happen to be more accurate and precise than the rotating Earth itself — our technology was better at keeping time than our planet was. This crossover allowed us to notice that Earth’s rotation rate is, in fact, slowing down.

Read the whole explanation after the jump.

Dear Facebook Universe,
Today marks the 26th time a Leap Second will be added to the calendar.
In the second half of the 20th century, we started tracking time via atomic clocks, which happen to be more accurate and precise than the rotating Earth itself — our technology was better at keeping time than our planet was. This crossover allowed us to notice that Earth’s rotation rate is, in fact, slowing down.
The primary culprit here is the Moon, whose tidal forces on Earth create friction between the sloshing oceans and our north-south coastlines. In response, the Moon’s orbit is spiraling away from Earth at a rate of about 2-inches (4cm) per year.
Such is the layout of this cosmic ballet — choreographed by the forces of gravity.
Several other factors also influence Earth’s rotation, but can serve to either slow us down or speed us up. In all cases it involves the re-distribution of mass on Earth’s surface, changing our planets rotation properties. These includes the freezing and melting of glaciers, mass migrations of animals, the buildup of new dams, and earthquakes.
Three ways to accommodate this fact: 1) Ignore it altogether. 2) Redefine the length of the Second, as necessary, to keep the total number of seconds the same, no matter the length of the day. Or 3) intermittently add “leap” seconds to compensate.
If we did (1) then eventually, clock time will not make sense relative to what the Sun is doing. If we did (2) then all the measurements that now depend on the precise definition of the second would be cast into flux. So we choose option (3). Beginning in 1972, on June 30 or December 31 (or both) we’ve added 25 leap seconds, as necessary. Today is such a day.
Beginning in 1972, on June 30 or December 31 or both, we’ve added 25 leap seconds, as necessary. Today is such a day.
Leap Seconds appear in the final minute of the last hour of today, Greenwich Time. For the Eastern Time Zone (North America) this corresponds to 7:59 PM. That minute will have 61 seconds in it. Something I’ve celebrated each time with a very tiny bottle of champagne.
Whatever you do, don’t waste it.
As always, Keep looking up.
-Neil deGrasse Tyson, New York City