Centuries ago cities designated 12 P.M. as the moment the sun reached its apex overhead, known as solar noon. But by the late 1800s it had become inconvenient for nearby municipalities to use slightly different times. Countries adopted time zones so large regions would be in sync (multicolor map). This practice creates offsets, however, between solar noon and clock noon. The offsets map (blue and red) reveals how much later (red) or earlier (blue) solar noon happens compared with clock noon on the summer solstice. In most places, the sun peaks later than 12 P.M.—which also means our clocks say sunrises and sunsets are later than our ancestors experienced. The offset pattern is similar in winter but less pronounced because daylight saving time, observed by many nations, exaggerates the shift (inset map of Europe).
This article was originally published with the title "Noon It's Not" in Scientific American 320, 3, 76 (March 2019)