As I type this, we’ve begun Daylight Savings Time. Although my family likes it, I don’t. I have to drive through deer and hog country, and Daylight Savings Time mornings in the spring and fall means that’s in the dark. My family likes it because it moves sunset up an hour according to the clock, and it seems that most people agree with them. There’s a move here to stay of Daylight Savings Time all year long, which means a late sunrise in the winter. Such has been tried in the US before, the last time to “save energy” in the 1970s, and it turned out to be a huge fiasco. Those of us who lived through it remember that, but who listens to us?
How we coordinate time is a matter of convenience, anyway, For thousands of years, every place determined its own time based on the sun. It’s also been known for thousands of years that if the sun was at it’s highest point in one place, it wouldn’t be at its highest point east or west of that location. That’s because the earth rotates from west to east, with each place moving beneath the sun. But since travel and communications were so slow, this really didn’t matter. Even when accurate time measurement became possible, every place determined its own local time.
It was only when people could travel hundreds of miles in a day and communicate over the same distance almost instantaneously that time coordination became important. Railroads had the issue of scheduling, where even a few minutes difference could mean disaster, and they adopted time standardization along their routes, and, in turn, zones where all railway clocks were set to the same time. In the US, this ended up with coordination between railways, and ultimately, in 1883, unified time zones defined by railroad terminals. Many towns adopted the railroad standardization, though there were protests against abandoning local time for “railroad time.” In 1918, the United States adopted time zones by law, courtesy of the Standard Time Act, and we’ve had time zones in the US ever since.
The calculation of time zones is straight-forward. The earth, on average, takes 24 hours to rotate 360° in respect to the sun. This means that in one hour the earth rotates 360°/24 hours = 15°. So, if a sundial in Greenwich, England, read 12:00 PM, a sundial 15° further west would read 11:00 AM while a sundial 15° further east would read 1:00 PM.
Longitude is measured from the Royal Naval Observatory in Greenwich, England, which is set at 0° longitude. Since the earth rotates 15° per hour in respect to the sun, a time zone centered at Greenwich, England, should extend 15°/2 west and east of 0° longitude. 15°/2= 7.5° = 7° 30 minutes, or 7° 30’. Technically, the next time zone should start at 7° 30’ and extend to 7° 30’ + 15° = 22° 30’, and so on.
Knowing this, we can calculate a theoretical time zone for a location by adding 7° 30’ to the longitude, dividing the result by 15°, and taking the whole number of the quotient. For example, Atlanta, Georgia is centered about longitude 84° 23’ 24” west. Adding 7° 30’ gives us 91° 53’ 24”. Dividing that by 15° gives us. 6° 7’ 33.6”. That means that theoretically Atlanta, Georgia, should be in the 6th time zone west of 0° longitude, which is the Central Time Zone in the US. But if you check a time zone map of the US, you’ll find that Atlanta is in the Eastern Time Zone, with the boundary between Central and Eastern time zones set at the Alabama – Georgia line. Theoretically the Eastern Time Zone should be centered on 75° west (15° x 5 = 75°), which means the theoretical boundary between Central and Eastern time zones should be 75° + 7° 30’ = 82° 30’ west.
Theoretical isn’t necessarily convenient, and that’s the entire point of time zones: convenience in coordinating time. That’s why the boundary between Central and Eastern time zones is the Alabama – Georgia line instead of running through the middle of Georgia. Tennessee, which is split by Central and Eastern time zones, has the boundary further west than 82° 30’ west, and so on. If you compare a map of time zones of the United States with a US map showing longitude, you might be surprised where the time zone boundaries are set. But while it might not be technically accurate, these boundaries are drawn to meet other criteria. For this reason, all of Alaska is now in one time zone.
Though time zones are convenient, it means that time by the sun seldom agrees with the clock. For Atlanta, if a sundial is set up at 84° 23’ 24” west longitude, it would be (84° 23’ 24” – 75°)/15° = 0.626 hours behind Eastern Standard Time. That’s 37 minutes, 33.6 seconds, or 00:37:33.6. That means noon, mean local time, occurs at 12:37:33.6 Eastern Standard Time, and at 1:37:33.6 Eastern Daylight Savings Time. But there’s another wrinkle: Since the earth is in an elliptical orbit, that means sometimes it moves faster and sometimes slower as it goes around the sun. The earth is also tilted in respect to its orbit, and this also has an effect. All this means that it might take a little more or a little less than 24 hours for the sun to reach its highest point on consecutive days. This is known as the Equation of Time. For March 15, 2022, a sundial should be about 8 minutes, 53 seconds slow. For Atlanta, this means noon by the sundial should occur about 12:37:33.6 + 8:53 = 12:46:26.6 PM Eastern Standard Time. Adding an hour for Daylight Savings Time, 1 + 12:46:26.6 PM = 1:46:26.6 PM Eastern Daylight Time.
Until maybe about a century ago, the Equation of Time was very important to time keeping. If you knew that your sundial was 9 minutes slow on a given day and the sundial said the time was 11:00, you knew to set your mechanical clock to 11:09. Almanacs used to list a column of sun fast or slow, and that was a handy reference. Some almanacs still list it.
In our time all this might sound strange and cumbersome. Yet how we keep time is as much what we’re accustomed to as it is convenience. Many people preferred local time over “railroad time,” and later government mandated time zones. The advent of radio broadcasts in the 1920s might have changed that, as listeners could set their clocks by the radio station rather than a sundial or a trip to town. Even in the 1970s (at least locally), radio stations would often play a beep to denote the exact time, maybe at noon just before the news broadcast, and it was easy to set your clock or watch by it.
These days I set my clocks and watches by a radio-controlled clock that picks up the National Institute of Standards and Technology (NIST) broadcast from WWVB, Fort Collins, Colorado, or by listening to their WWV time signal broadcasts on shortwave (2.5, 5, 10, and 20 MHz). Others are content to use the time on their cell phones. It all comes down to what we consider the most convenient.
This brings us back to Daylight Savings Time, specifically keeping it in place all year. Based on my experience in the 1970s, it would be very inconvenient, and I think people now would think the same once they lived through it. Perhaps not. Still, I can take some comfort in knowing that the day will come when I’ll be retired and can sleep in, which for me means getting up at dawn.
Who knows? Maybe that will change my opinion of Daylight Savings Time.
I began to doubt the accuracy of my comment about almanacs listing sun slow and fast. The modern Old Farmer’s Almanac does, but what of earlier ones. A check of an 19th Century copy Old Farmer’s Almanac did, but other period almanacs I checked didn’t.
I found a reprint of the first Poor Richard’s Almanac, published for 1733, and it, too lacked a sun fast and slow column. But under “Explanation of this Almanack” (sic), I found the following:
“I have chose to put the Sun’s rising and setting for every day, rather than the Moon’s, because of its constant use in setting of Clocks and Watches.”
This would mean that Poor Richard’s Almanac listed times in mean solar time for Philadelphia, Pennsylvania, otherwise, all a Philadelphian would have to do would be to set their clock or watch directly by the sundial. According to this edition of Poor Richard’s Almanac, setting clocks and watches by the sun rise and set in an almanac was a common practice.
This raises another question: If people were setting their mechanical timepieces by sunrise and sunset, did they need a sundial at all?
On Daylight Savings Time
When I wrote this post, I had no idea that there was a bill before Congress to make Daylight Savings Time permanent in the US. On March 15, 2022, the Sunshine Protection Act passed the Senate by unanimous vote. The bill must still be passed by the House of Representatives before it can go to the President.
The last time the US went to permanent Daylight Savings Time was in 1974. After the continental US experienced winter with late sunrises, there was such an outcry that it was repealed in 1976.
Hmm…back in 1974, we had inflation, rising gas prices, and tensions with the Russians. If everyone’s feeling nostalgic for the 1970s, this isn’t the way to do it.