Why the earliest sunset occurs before the winter solstice

We are now less than two weeks away from the winter solstice, also known as the shortest day of the year in terms of daylight. Don’t let that fool you into thinking the sun will set at it’s earliest time on that particular day, though! The earliest sunset of the year will actually occur today, December 8th!

Why don’t these two events align? It has to do with the differences in the timekeeping methods that we use compared to how time is measured using the sun, also known as the equation of time.

The length of a solar day is not precisely 24 hours long and varies throughout the year because of the elliptical shape of Earth’s orbit and its tilt. During the winter and summer, it is longer than 24 hours and shorter than 24 hours during the spring and fall.

Solar time is also called sundial time because it is measured using the sun’s angle in the sky in respect to Earth’s surface. If you were to take a picture of the sun each day when your traditional clock says noon, you’ll quickly notice that the sun is not always at the same place in the sky. It will vary depending on the variation in the length of the solar day, and it moves north and south with the change of seasons.  All of this ties back to the elliptical orbit that Earth has.

Beyond December 8th the sun will begin setting later and later each day, however, we won’t actually start gaining daylight until after the winter solstice on December 21st. If you are not a fan of winter, at least you can start looking forward to longer days in the next few weeks! Granted the change is not all that noticeable right now, but once we get through January and February you’ll easily notice the longer days as the spring equinox nears next year.

Meteorologist Andrew Stutzke

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