Want to know a silly thing about time? The clocks we use are so precise that every so often, we have to adjust them because they are too precise for the rotation of our planet.
The rotation of our planet is slightly slower than our “precise” time. For example, the clocks that keep time in the United States, Russia, China, Zimbabwe, Peru, and all other places, never slow down. They always keep the same pace of time no matter what. These are atomic clocks and they are extremely accurate.
They are so accurate that they don’t always align with the time it takes for the sun to rise and fall for a given solar day.
If I were to ask you how long a day is, what would you say?
If you answered 24 hours, you are short by 0.0000006 seconds. Our day is actually just a little longer than 24 hours, but this extra time is so small it almost doesn’t matter. Almost…
Over time, this extra time adds up. Meanwhile, the clocks we use to measure time never really change. After a while, our atomic clocks get too ahead of the sun. When that happens, we have to add an extra second to the clocks that we use. We call these: leap seconds.
They sound similar to something you may have heard of: the leap year. Do a bunch of leap seconds add up to a leap year? I’m afraid not. Leap years happen because of the relationship between the earth and the sun, whereas leap seconds happen because of the relationship between the earth and the moon.
The moon is large enough to affect the Earth’s rotation. The pull that the moon has on the earth is called the “gravitational pull”. This gravitational pull creates a big bulge of water. That bulge of water is so large, you can’t really see it. Instead, we see the water changing along the shores. We call these tides.
You may hear people say that “the tides are rising” or “the tides are falling”. It’s not really that the water level is changing, it’s that the earth is rotating into and out of the bulge of water. If we are rotating into the bulge of water, the tides look higher, and if we are rotating out, the tides look lower.
Tides rising and falling by McGill University
Because the moon is collecting all this water with its gravitational pull, it affects the speed of the earth’s rotation. Think of the tides as dragging the earth a little bit. This drag (and other forces) makes the rotation of the earth less precise than our clocks would have us think.
There is nothing slowing our atomic clocks down, so they get ahead of our planet’s rotation. When our clocks get too ahead, that’s when we humans insert another second into our clock’s day.
We humans have only been doing this for about 50 years, but many meteorologists have agreed to stop using leap seconds by 2035. But it is not clear how we will keep track of these differences in our clock time and our solar time after that.
My question to you is: are our clocks so precise that they become imprecise?
