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Yesterday was shorter than usual.
Because the earth was rotating unusually fast, our day was 24 hours minus 1.42 milliseconds. The day lasted 23.9999996054 hours.
The other shorter days this summer will be July 22 and August 5. Meanwhile, July 5, 2024 was a record setter when the earth’s rotation was 1.66 milliseconds faster than the standard 86,400 seconds.
Length of the Day
According to Time and Date, during the 1870s, the days were shorter while in the early 1900s, a slower earth meant they were longer:
Leap Seconds
Because our clocks are exact but the earth is not, little by little the time creeps away from where it should be. Doing nothing, eventually we would be having lunch in the moonlight. For that reason, the world needs a leap second.
Although one day and night are supposed to last for 86,400 seconds, the total is closer to 86,400.002. So, to maintain a clock and sun sync, during 1972 we added 10 leap seconds and since then, 27. With the addition of the last leap second on December 31, 2016 at 23.59.59, the clocks went to 23:59:60 rather than 00.00.00.
Sadly, in 2035, they will abandon the leap second. The reason relates to the hassle of the addition by those of us that need to know the exact time. It is possible though that seconds will be added less frequently.
So we could wind up with a deci-leap day?
Our Bottom Line: Standardization
Whether looking at weights and measures or leap seconds, we are really talking about standardization. A shared system of weights, measurement, and time enables commerce to function efficiently,
In the U.S., Thomas Jefferson was wise enough to encourage standardization in his 1790 report to Congress. Continuing the principle that the federal government is responsible for uniformity, the National Institute of Standards and Technology (NIST) was established in 1901 (as the National Bureau of Standards).
As for the time, it took the railroad to establish some uniformity. Traveling from town to town during the 1830s meant constantly changing your watch (if you had one). By the 1850s, though, local time started becoming railroad time. The invention of the telegraph enabled the same time to be communicated from place to place.
As a result, railroads gave their employees “a good watch” that had the same time. Once the stations had the time, so too would the town. To make a long story quite short, today we have the time zones that established the same time.
But, without the leap second, they won’t quite be accurate.
My sources and more: Thanks to the BBC’s World Business Report for alerting me to our shorter day and Yahoo and Time and Date for more of the facts. But if you have more time, Keeping Watch: A History of Time is the book to read.
Please note that, as an update, today’s post included vast sections of a past econlife on leap seconds.
1 Comment
Will we eventually need a leap minute? Yes, because, although tiny random day-length variations are caused by earthquakes, ocean current variations, there is actually a long-term secular slowing of earth’s rotation. The reason is that, despite the fact that simple physics decrees that tidal bulges must be directly toward and opposite the earth-moon line, the material of those bulges must flow to get there. Friction from that flow makes a torque that opposes the earth’s rotation.