Have you ever had the feeling that the days are getting shorter and shorter?
The fact is, you’re right, if only partially.
This year, we live the shortest day on record: June 29.
But before checking your calendar to see if it was one of those “you didn’t have time” days, try to guess how short it was.
Not for hours, not minutes, not even seconds.
According to timeanddate.com, a website with resources for measuring time and time zones, the Earth took 1.59 milliseconds less to rotate on its axis on June 29.
Or rather, June 29 was 1.59 milliseconds shorter than 24 hours.
To give you an idea, a blink of an eye lasts 300 milliseconds. In other words, the time you wasted on this day is just over the 300th part of a blink of an eye, and it’s only possible to perceive with very precise instruments.
Do you understand now why you are right, but only in part?
But why would the Earth’s rotation be accelerated?
And if we’re seeing shorter and shorter days, does that mean it could speed up even faster?
The length of days on Earth is measured by rotational motion, or how long it takes for the planet to rotate on its own axis.
And thanks to atomic clocks, we can measure those days with an accuracy we couldn’t achieve otherwise.
An Earth day — or a period of rotation — should theoretically last 86,400 seconds, which are the seconds that exist in 1,440 minutes or 24 hours.
But since the year 2020, things have been weird.
Earth is accelerated
As of 2020, the “shortest” day on record was July 5, 2005, lasting 1.0516 milliseconds less than 24 hours.
But in 2020, Earth recorded the shortest 28 days known since atomic clocks came into use in the 1960s.
On July 19 of that year, the planet broke the record it had set in 2005, recording a day 1.47 milliseconds shorter than normal.
The new record, from June 29 this year, is 1.59 milliseconds shorter than normal.
But it is something that scientists believe is not a cause for concern.
“We believe this has been going on for millions of years, but with very small variations,” Graham Jones, an astrophysicist at Time and Date, tells BBC News Mundo, the BBC’s Spanish-language news service.
And Christian Bizouard, from the Paris Observatory of the Earth Orientation Center of the International Earth Rotation and Reference Systems (IERS), adds that the acceleration trend we see today started in the 1990s.
“After an interruption in 2004, with a small deceleration, the acceleration resumed in 2016”, details Bizouard.
But scientists aren’t sure how long this acceleration can last.
“At some point, things will slow down again,” says Jones.
“On time scales of decades (between 10 and 100 years), the length of days shows irregular variations”, explains Bizouard to BBC News Mundo.
Scientists agree that these changes are caused by the interaction of factors such as the activity of the planet’s molten core and the movement of the oceans and atmosphere.
But, in fact, the origin of these variations is not understood, says Bizouard.
Jones also acknowledges that experts don’t know “exactly why the Earth speeds up or slows down for long periods of time.”
But in general, for Jones, “the accuracy of the Earth as a ‘timer’ is surprising”, since “only a few milliseconds are lost”.
What would happen if the Earth lagged behind or advanced further?
Even though they are small, changes in Earth’s time can add up over the years and cause our clocks to move forward or backward by a second.
To correct the mismatch, scientists have used the so-called “leap second” since 1973, which can be positive or negative.
That is, this second can be added to our clocks when the Earth is late, or it can be taken away when the planet finishes its rotations in less time than usual.
Since 1973, the IERS has added 27 leap seconds to the official time of clocks on Earth.
“If the shorter days continue, at some point we may need a negative leap second, that is, take a second off our clocks to adjust to the faster rotation of the Earth,” says Jones.
“But we may or may not need to. We don’t know if that will happen because we don’t know how long this trend will last or if it will last”, he adds.
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