The last minute of this month will be longer!

On June 30, the minute that separates 11:59 p.m. to midnight in Coordinated Universal Time or UTC, will be unusually 61 seconds longer instead of the usual 60 seconds. Reason: the rotation of the Earth is irregular. Our planet has a tendency to slow down due to the gravitational pull of the Sun and the Moon. It therefore creates a gap between the Universal Time, based on the rotation of the Earth and the International Atomic Time, which is established from atomic clocks developed by man.

In a somewhat rare occurrence known as a "leap second," time will stop briefly on June 30 to align with the rotation of the Earth. Credit: GUILLAUME Souvant / AFP
In a somewhat rare occurrence known as a “leap second,” time will stop briefly on June 30 to align with the rotation of the Earth. Credit: GUILLAUME Souvant / AFP

26 seconds since 1972

By this second additional, Human hears reconcile two time scales , that of Universal Time (UT) based on the rotation of the Earth and its position relative to the stars and that of the International Atomic Time (TAI), defined since 1971 From the world of atomic clocks park. When the Coordinated Universal Time (UTC) was created in 1972 by an international agreement, it was agreed that the gap between the two should not exceed 0.9 seconds. Beyond that, a leap second to be inserted into the UTC time. Since that time, 26 seconds (counting that of 30 June) have been added , most recently in mid-2012 and the last second is in 2008.

The Earth slows

“In January, we warned the world should be adding a second on the night of 30 June to 1 July,” said Daniel Gambis, whose service is a branch of the Service Rotation Earth and systems Reference (IERS). ” The Earth rotates fancifully as atomic clocks are drastic ” adds this astronomer. On the very long term, the blue planet tends to slow down , due to the gravitational pull of the Moon and the Sun, head of tides. It is also sensitive to hazards associated with air movements, changes in ice sheets, earthquakes … The current atomic clocks, which rely on the properties of atoms to measure time, however, are of such accuracy they would record a second drift every 300 million years.

Who will recognize the pause? 

Most of us won’t notice the addition, which happens at 23:59:59 coordinated universal time (UTC), or 7:59 p.m. ET, unless we deal in timescales shorter than a second, or if we use a computer program that crashes because it can’t handle the leap second. It’s happened before: The 2012 leap second brought down Reddit, Gawker Media, and Mozilla.

Not everyone recognizes the leap second, although Apple does so on its devices. Google mobile devices sync with internet time services that are usually tied to atomic clocks. But “if you have a standard Windows system, [it] just ignores the leap second,” says Judah Levine, a physicist at the National Institute of Standards and Technology (NIST) in Boulder, Colorado.

Financial markets like the New York Stock Exchange also take the leap second into account. The exchange will close the market a half hour earlier than normal, at 7:30 p.m. ET on June 30, to help their systems deal with the addition.

Navigation services, like the U.S. Global Positioning System (GPS), never use leap seconds, Levine says. That’s because they need accurate measures of time in their calculations. If they stopped their internal clocks for the leap second, they would get inaccurate positions.

The end-user isn’t aware of this because the GPS system will still send information to the receivers we use—whether it’s something we’ve picked up in an outdoor equipment store or our smartphones—about the leap second. So we’ll see the correct time on our devices. But “true GPS time is off from civilian time by something like 16 seconds,” says Levine.

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