As long as it doesn’t break the internet, the leap second to be added tonight might not seem like a big deal. However, the existence of a leap second indicates something very fundamental about our philosophy of measurement itself. To wit: what happens when your measuring tools outperform the thing the are meant to measure? Back in the early days of trains, you could “set your watch” by the arrival of a locomotive. Now, with your atomic clock linked smartphone, you would more likely conclude that the train was late. The latest generation of atomic clocks won’t gain or lose a second for hundreds of millions of years. So we can observe directly the fact that the Earth’s rotation is slowing, which will, over time, cause the day/night cycle to fall out of sync with our clocks. Why does this bother us? We could skip intercalation entirely and let time slip, just like the lunar calendar compared to the solar. For example, it happens to be Ramadan right now, which is tough for adherents in the Northern Hemisphere who are experiencing long periods of daylight. Since 12 lunar cycles equals 354 days, it cycles around the seasons. Other calendars, called lunisolar, add intercalated “leap months” to keep the lunar-based holidays more or less in sync with the solar year. The fact that we contrive for our wristwatches to keep time that corresponds with the sunrise shows that time – and all measurements – are constructs for our convenience.
Lastly, if you are unsure what to do with your extra second, John Oliver is here to help.