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Scientific American

March 1, 2021

1 min read

Sunlight Changes Unequally All Year Long

Some days we gain one minute; some days we gain three

By Mark Fischetti & Jen Christiansen

Detail of graphic that shows variable rates in losses or gains of sunlight each month at different latitudes.

Jen Christiansen

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People who live in the midlatitudes enjoy maximum daylight on the summer solstice and put up with maximum darkness on the winter solstice. Between the two extremes, sunlight increases or decreases each day, but the rate of change is not steady. It is least in midsummer and midwinter and greatest around the spring and fall equinoxes. The biggest shifts occur at very high latitude: Just before the period of total darkness (or just after total darkness), the sun is barely above the horizon around solar noon, when the solar elevation changes very slowly, resulting in a large daily difference in daylight minutes lost (or gained). People who live along the equator see no change; they experience a steady 12 hours of day and night throughout the year.

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Credit: Jen Christiansen (graphic), Mapping Specialists (globes); Source: NOAA Solar Calculator

Rights & Permissions

Mark Fischetti has been a senior editor at Scientific American for 17 years and has covered sustainability issues, including climate, weather, environment, energy, food, water, biodiversity, population, and more. He assigns and edits feature articles, commentaries and news by journalists and scientists and also writes in those formats. He edits History, the magazine's department looking at science advances throughout time. He was founding managing editor of two spinoff magazines: Scientific American Mind and Scientific American Earth 3.0. His 2001 freelance article for the magazine, "Drowning New Orleans," predicted the widespread disaster that a storm like Hurricane Katrina would impose on the city. His video What Happens to Your Body after You Die?, has more than 12 million views on YouTube. Fischetti has written freelance articles for the New York Times, Sports Illustrated, Smithsonian, Technology Review, Fast Company, and many others. He co-authored the book Weaving the Web with Tim Berners-Lee, inventor of the World Wide Web, which tells the real story of how the Web was created. He also co-authored The New Killer Diseases with microbiologist Elinor Levy. Fischetti is a former managing editor of IEEE Spectrum Magazine and of Family Business Magazine. He has a physics degree and has twice served as the Attaway Fellow in Civic Culture at Centenary College of Louisiana, which awarded him an honorary doctorate. In 2021 he received the American Geophysical Union's Robert C. Cowen Award for Sustained Achievement in Science Journalism, which celebrates a career of outstanding reporting on the Earth and space sciences. He has appeared on NBC's Meet the Press, CNN, the History Channel, NPR News and many news radio stations. Follow Fischetti on X (formerly Twitter) @markfischetti

More by Mark Fischetti

Jen Christiansen is author of the book Building Science Graphics: An Illustrated Guide to Communicating Science through Diagrams and Visualizations (CRC Press) and senior graphics editor at Scientific American, where she art directs and produces illustrated explanatory diagrams and data visualizations. In 1996 she began her publishing career in New York City at Scientific American. Subsequently she moved to Washington, D.C., to join the staff of National Geographic (first as an assistant art director–researcher hybrid and then as a designer), spent four years as a freelance science communicator and returned to Scientific American in 2007. Christiansen presents and writes on topics ranging from reconciling her love for art and science to her quest to learn more about the pulsar chart on the cover of Joy Division's album Unknown Pleasures. She holds a graduate certificate in science communication from the University of California, Santa Cruz, and a B.A. in geology and studio art from Smith College. Follow Christiansen on X (formerly Twitter) @ChristiansenJen

More by Jen Christiansen
Scientific American Magazine Vol 324 Issue 3This article was originally published with the title “Daylight's Uneven March” in Scientific American Magazine Vol. 324 No. 3 (), p. 76
doi:10.1038/scientificamerican0321-76
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