Maybe it’s the unstoppable, gradual changing of the seasons, shortening or lengthening the amount of sunlight in the day. Or maybe it’s that feeling that time is speeding up with age. Or maybe it’s just Friday. Whatever the cause, days here on Earth never really seem to feel like they’re the same length. But, actually, that’s true: days on Earth aren’t all the same length.
We’ve known for a long while that the Earth wobbles as it rotates. The gravitational pull of the Moon is slowing our planet down. Even the motion of the ocean can have an effect. It’s the reason scientists long ago stopped relying on the rotation of the Earth as a reliable measure of time, turning to atom clocks instead.
We know about all these things, and yet still the length of the day was changing in ways we didn’t understand. According to New Scientist:
Three times in the last decade Earth’s spin has missed a beat. These seemingly random blips cause days to temporarily stretch and shrink.
For reasons unknown, something in the Earth causes the planet’s rotation to shift its pace. Aside from the persistent drag of the Moon, or the eccentricities of our planetary rotation, or the drag of the wind and water flowing over our surface or pushing against mountain ranges—aside from all that, writes Mark Viney for New Scientist, “Three times in recent years – in 2003, 2004, and 2007 – our planet’s spin has stuttered. The jumps interrupt the longer-term changes by a fraction of a millisecond, and last several months before going back to normal.”
According to the scientists, they don’t really know what causes the blips in day length. Their best guess, they write, is that part of the fluid core deep inside the Earth could glob on to the mantle, changing the balance of the Earth and sending the rotational rate askew.
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