Yesterday was November 3, 2020 and Election Day in the United States. Spoken and written about ad nauseum, the United States is a divided country. Although the 2020 election is the latest reminder of this, presidential elections have demonstrated this for at least the past two decades, going back to Bush v. Gore in the year 2000. And it is not just political differences that divide the country: cultural, religious, and financial differences create barriers to integration. Even time differences divide the country into multiple time zones!
Speaking of which, having just passed November 1 in which most of the country turned back their clocks one hour, I wanted to examine how the length of the day changes throughout the year. For me, sunlight and interior natural light is super important. I love long days and summer is my favorite time of year partially because of this (I also like hot weather). Conversely, autumn is my least favorite season because the days get shorter. Turning back the clocks in early November is just another sign of how precious sunlight is during the day.
On the other hand, I have heard (horror) stories about the “endless nights” during winter in northern cities such as Alaska and Scandinavia. In fact, I experienced the opposite — the “endless day” — back in 2012 when my partner and I lived in Denmark for the summer. It was surreal to be out at 11pm at night and still have the sun shining. For a heliophile like myself, are there areas of the United States that have more hours of sunlight than others on a consistent basis?
The Guiding (Chart of) Light
I know that sunlight during the day is based on the latitude of where you are on the earth. For the northern hemisphere, the further north you live, the more dramatic the difference will be between summer days and winter days in terms of sunlight than someone who lives further south. As mentioned above, for people who live above the Arctic Circle (around 66 degrees north latitude), they enjoy near 24 hours of continuous sunlight during the summer. Conversely, they also enjoy near 24 hours of continuous darkness during the winter.
However, what about the mid-latitudes where most Americans live, such as between 25 and 50 degrees north latitude? I used NOAA’s Solar Calculator to gather sunrise and sunset times for various American cities. I chose cities that were roughly 5 degrees different in latitude from each other in order to be representative of all American cities. I also included Honolulu — the most southern major U.S. city — and Anchorage — the most northern major U.S. city. I am interested in seeing the results of these extremes, especially Anchorage.
Well, the results were quite interesting to me in several ways! Yet let’s start with what is not surprising: the further north you go, the longer days you have during summer and the shorter days you have during the winter. Anchorage’s longest day during the summer is 19 hours and 23 minutes, almost 3 ½ hours longer than Seattle’s longest day and seven hours longer than Honolulu’s longest day. On the other hand, during the winter, Anchorage only receives 5 ½ hours of sunlight during the shortest day in December. In the tropics, Honolulu’s shortest day is about twice as long, coming in at just under eleven hours on the same day.
This is where things got interesting to me. Unlike Anchorage that has a dramatic difference between winter and summer days, Honolulu is relatively drama-free. Only 2 ½ hours of sunlight differs between Honolulu’s longest day and shortest day of the year; Anchorage has a swing of almost 14 hours! On the continental U.S., cities don’t have nearly as much of a difference between them, however still significant. Seattle has almost eight hours difference between its longest and shortest days, while balmy Miami is just over three hours.
Also, from a pure aesthetic point-of-view, I thought the sunlight curves of each city were beautiful. Each curve was smooth and if years were linked together, would look like sine waves. When plotted together, I found the chart quite pleasing to the eye, which I greatly appreciated. This blog after all is dedicated to the Joy of Charts so why not dwell on the beauty of the chart?
Conclusion: Perhaps Election Day should have been September 23
From a practical standpoint, for people who love the sun — or worse, suffer from Seasonal Affective Disorder (SAD) — moving to a city that has steady year-round sunlight may be beneficial to your well-being. Although the concept of midnight sun is cool for a vacation, the real-life issue of having 8 hours or less of sunlight during the winter is exactly what contributes to seasonal depression. Plus, for some of us, having sun too late at night may worsen the ability to go to sleep, meaning too long of a day actually affects us negatively!
The most surprising revelation I found from this data was that around the Spring and Fall Equinoxes — the days of the year that the Sun hits the northern and southern hemispheres equally — the length of the day across the United States is the same. Yes, whether you are in Honolulu, Anchorage, Los Angeles, New Orleans, or New York, the length of the day is around 12 hours and 5 minutes on these two days of the year. In the year 2020, they occurred on March 18 and September 23. Hence, twice per year, Americans are united in the amount of sunlight they receive. On Election Day, with the incessant news coverage of the election, perhaps this is something that we need to remind ourselves: there are things that can unite the country, such as the pure joy of the sun shining on your face during a brisk spring or autumn day. And twice per year, Americans can enjoy this in equal amounts.
Sources for Chart Calculations:
NOAA Solar Calculator: https://www.esrl.noaa.gov/gmd/grad/solcalc/
