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The trickery of daylight savings
When civilizations have told themselves that noon isn't noon
This past weekend, we marked the end of that preposterous annual ritual, daylight savings time. There are many ways, most of them confusing, to talk about what daylight savings is and how “time changes” when we spring forward and fall back. Let me cut through this confusion:
Daylight savings means that we work 8 to 4 rather than 9 to 5. That’s it.
There is only one moment in the day when the sun is “highest,” when shadows point due north or due south, or disappear entirely. Astronomers call this moment “local apparent noon.” The time period that elapses between two local apparent noons, the “apparent solar day,” is 24 hours (plus or minus about 30 seconds). Whatever we choose to call the hours of the day on our clocks, the planets spin on in their orbits, and local apparent noon comes at 24 hour intervals.
Imagine a place where local apparent noon is, on the clock, 12pm. This is called local solar time. As the seasons pass and the days get longer or shorter, the times of sunrise and sunset will move, but 12pm is always the time when the sun is highest (plus or minus 30 seconds).
Daylight savings was originally posed as a cost-saving measure: if we got up earlier, we would “save daylight” in the afternoon when people are more likely to be out and about. Once a year, we “spring ahead” and adjust all our clocks, and then we “save daylight” for the summer.
If you keep local apparent noon in your mind, it will become clear that “daylight savings” means that we all get up one hour earlier and start work one hour earlier. Rather than adjusting our clocks, we could instead say that our work hours in the summer are not 9 to 5 but rather 8 to 4. Local apparent noon, which is 12pm solar time, doesn’t move. It’s just that we stop eating lunch around solar noon and instead start eating it an hour before solar noon.
In other words, daylight savings is a massive piece of trickery. Imagine I told America, hey, it would be safer and more efficient if we all got up an hour earlier every day and then went out to dinner and to the club an hour earlier. I would be derided as a prude and a killjoy. But now imagine I told America we would “save” daylight by doing some magic with our clocks only twice a year?
The trickery is that we tell ourselves that we only lose one hour of sleep on one weekend in the spring, and we put that hour into some sleep bank, to be withdrawn when we “fall back.” But the reality is that, during daylight savings, we get up an hour early every single day. Our bodies know we are waking up an hour earlier every day, and they do not like it. Our bodies pay attention to the sun and they are not fooled by clocks.
Many people make claims about how daylight savings is better: because there is “more daylight” after work, we save energy, or we shop more, or we are less likely to be victims of crime. Rather than dispute the evidence for each of these cases, I ask instead: are any of those things worth getting up an hour earlier and starting work at 8am rather than 9am?
Setting your clock forward so you wake up earlier and get to work earlier is a piece of trickery worthy of a teenager with sleep deprivation or poor time management. It is not a way for us to run our entire society.
Before the Industrial Revolution, most people moved by the rhythms of the sun. The “day,” meaning the time between sunrise and sunset, was divided into twelve “hours.” The ancients knew from water clocks that these “hours” were not all the same duration: in the winter, an hour was shorter than in summer.
When more precise pendulum clocks arose in the Scientific Revolution, these clocks were set to match local apparent noon. When the sun was highest in the sky, the town clock would toll noon. This meant that clocks in different places were not all synchronized. The sun rises in the east, so local apparent noon comes earlier in places further east. Every quarter mile to the west along the equator delays local apparent noon by about one second.
Before the railroad, this asynchrony between town clocks wasn’t a bother. if you set out on a 10 hour journey from one town to another, it would not be particularly important if you “lost” or “gained” a few seconds, or even a few minutes, because the clocks in the two towns were not exactly aligned. With the Industrial Revolution and with the railroad, those seconds started to count. Trains were expected to be on time, down to the minute, so losing or gaining any time became problematic.
England was the first country with a widespread rail network, so it was the first place where clocks were synchronized to the same standard. The English railroad companies chose as their standard the time at Greenwich, the site of the Royal Observatory. Railroad companies in other places chose times relative to Greenwich, thus creating the precursors to our modern time zones. Later, the United States pushed for an international agreement about where zero degrees longitude should fall, and the obvious choice was Greenwich.
(The “mean” in “Greenwich mean time” was a resolution of a second problem that came from more accurate timekeeping: the time between subsequent local apparent noons is not exactly 24 hours. The Earth spins slightly faster when it is closer to the Sun and slightly slower when further away. So “mean” refers to the average duration of a day, averaged across the days of the year.)
In short, the last time we adjusted our relationship with time, when we accepted a “standard” time distinct from local solar time, it was for a pretty good reason. Our world is confusing enough with time zones, and it’s hard to imagine a world where clock time differed between individual cities. It wouldn’t be that a television show starts that “9pm Eastern, 8pm Central” but rather at “9pm Boston, 9:08pm New York City, 9:17pm DC” and so forth.
But I do find it very easy to imagine a world where 12pm is always some approximation of apparent noon. This is the world where we abolish daylight savings. If we all want to start work at 8am rather than 9am in the summer, so be it. But let’s call a spade a spade.
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