30 June, Tuesday, will be one second longer than any other day this year—and the longest day since 2012. That’s because, as Nasa explains, a “leap second” will be added to the clocks to account for the fact that the Earth’s rotation is gradually slowing down.
While it’s highly fascinating that we get one extra second of life (I’m over the moon at the thought), I’m more curious to find out why the Earth is suddenly slowing down?
Naturally, none of us has been able to feel the change in Earth’s rotational speed. However, scientists who are always on the lookout for extraordinary things and observing every little change, noticed
this a while back. They claim it is due to a transfer of Earth’s rotational momentum to the Moon’s orbital momentum – as tidal friction is slowing the Earth’s rotation. That increase in the Moon’s speed is causing it to slowly recede from Earth (about 4 cm per year), increasing its orbital period and the length of a month as well. It’s a difficult concept to grapple…a simple example might help”
To picture what is happening, imagine yourself riding a bicycle on a track built around a Merry-go-Round. You are riding in the same direction that it is turning. If you have a lasso and rope one of the horses, you would gain speed and the Merry-Go-Round would lose some. In this analogy, you and your bike represent the Moon, the Merry-Go-Round is the rotating Earth, and your lasso is gravity. In orbital mechanics, a gain in speed results in a higher orbit.
The slowing rotation of the Earth results in a longer day as well as a longer month. Once the length of a day equals the length of a month, the tidal friction mechanism will cease. (ie. Once your speed on the track matches the speed of the horses, you can’t gain any more speed with your lasso trick.)
That’s been projected to happen once the day and month both equal about 47 (current) days, billions of years in the future. If the Earth and Moon still exist, the Moon’s distance will have increased to about 135% of its current value.