Earth will spin slightly faster on Tuesday making the day a fraction of a second shorter
Tuesday will be an exceptionally short day by just 1.25 milliseconds. The Earth will spin slightly faster on its axis than usual, the third such acceleration this summer, according to astronomers.
“Tomorrow’s day will be about 1.25 milliseconds shorter than normal,” Katrien Kolenberg, professor of astrophysics at the University of Amsterdam and the Vrije Universiteit Brussel (VUB) told VRT NWS. “A difference shorter than the blink of an eye.”
Instead of taking the usual 86,400 seconds to complete a full rotation, the Earth will finish in 86,399.9875 seconds. These occasional "speed-ups" are not unusual, but scientists have noticed they are becoming more frequent.
Tides, winds and the Earth's core
The Earth can change speed based on shifts in mass and energy. One reason for the acceleration is that the moon is currently slightly further from the equator, altering the pull of the tides.
Seasonal weather patterns also play a role. In summer, air pressure systems and upper-atmosphere winds affect the planet’s rotation. Meanwhile, subtle movements deep within the Earth's core can also influence surface speed.
The planet’s rotation has generally been slowing over the past 4.5 billion years. In its early days, the Earth completed a full spin in just 10 hours. Around 1.5 billion years ago, days lasted 20 hours. The trend continues because the moon is gradually moving away from Earth, weakening its gravitational pull and slowing the planet’s rotation.
Since 1972, a leap second has been added 27 times to keep our clocks in sync with Earth’s slowing spin. But if accelerations become more common, scientists may eventually have to subtract a second, in what they refer to as a negative leap second.
Why milliseconds matter
While people won’t feel any difference, the change is significant for technologies that rely on ultra-precise timing. GPS satellites, for instance, travel at high speed and require accurate timekeeping to function properly. “In a single millisecond, they will cover a great distance,” said Kolenberg.
It is not yet clear how systems would handle a negative leap second. As with the Y2K scare at the turn of the millennium, many are not designed to deal with such an adjustment.
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