(that’s two weeks later) nor the one with the earliest sunset (two weeks before).

During the winter months, the solar day—the time from solar noon (when the sun is highest in the sky) to the next solar noon—is longer than 24 hours. Since your clock sticks with its regular, boring, 24-hour cycles, solar noon comes a bit later each day.

On January 1, for example, solar noon is 28 seconds later than on December 31 (relative to when your clock says it’s noon, that is). But January 1 also has more daylight—in the Northern hemisphere, sunrise comes 16 seconds earlier than the day before. Combine those two effects, and—again, according to your thick-headed clock—the sun seems to rise 12 seconds later than it did on December 31.

So that’s when you get daylight; where the sun is also changes. That’s why solar noon moves: Earth orbits the sun—duh—but over the course of the year, the sun appears to make its way around us on a path called the ecliptic. And each day, Earth has to rotate a wee bit farther around its axis to make a full rotation relative to the sun. (Watch it at the same time from the same spot on Earth every day and the sun traces an analemma, shown above.)

It gets weirder. In winter, Earth’s elliptical orbit carries it closer to the sun, which then covers a larger angle in the sky—and seems to move faster. And the 23.5-degree tilt of Earth’s axis slows the sun in spring and fall, but not winter or summer.

Sound complicated? Don’t worry. Here’s how scientists figure out when the sun is really going to rise.

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Authors: Julie Rehmeyer

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