Measuring Time: Why a new years countdown ain’t what it used to be
How do you measure time?
It’s a simple enough question: look at a watch, clock or cell phone. But how do those devices keep track of seconds and ensure that each second is the exact same amount of time?
There’s a long and interesting history for how humans answered this question over the last ~2,000 years. But this story starts in 1895 when Simon Newcomb published a book called, “Newcomb’s Table of the Sun” which mathematically calculated the Earth’s position relative to other celestial bodies in the universe.
In 1956, The International Astronomical Union realized that the accuracy of the calculations made by Newcomb could be used to increase the precision of time measurement. Since celestial bodies movements are governed by the laws of physics their motion would always be consistent, creating a universal basis for time measurement. The observations made from 1750 to 1892 on the Earths position and movement were used to create a new calculation for the second.
Now that there was an accurate data set to draw on, a second was defined as a fraction of the total amount of time it took the Earth to complete 1 revolution of the sun in the year 1900 (e.g. 1 year). Functionally this meant that 1 second was equal to 1⁄31,556,925.9747, or 1 over the total amount of seconds in a year.
Everyone was very pleased with themselves, until there was a troublesome discovery about the nature of the Earths rotation:
The Earth’s rotation is slowing down.
If a second is based on a year (1⁄31,556,925.9747) in 1900, and a day in 2019 is longer than a day in 1900….there’s a big problem.
Many debates were had: do you stretch a second out? Do you add a second? Do you change the system all together?
in 1965 the decision was made to add a leap second on December 31 whenever the difference between the atomic clock and observed solar time exceeded 0.9 seconds.
While there are no leap seconds scheduled for December 31st, 2019, keep this history in mind when the clock strikes midnight. It’s taken thousands of years of work for everyone to be able to say, “Happy New Years!” at the exact same time.
