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SPOKANE, Wash.– Saturday is the shortest day of the year, but it’s not our earliest sunset, nor our earliest sunrise? Why is that?
Earth orbits the sun in an oval, not a perfect circle. This means the planet moves at different speeds at different times of the year. From our perspective on Earth, this results in the sun taking slightly more or slightly less than 24 hours to return to the same point in the sky.
From early November to early February, the sun appears to move slower across the sky than at any other time of the year. This shifts sunrises, sunsets, and midday sun by 14 minutes over the course of these months. However, sunsets still occur earlier each day at the beginning of December because Earth continues to tilt away from the sun, lowering it in the sky.
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As the winter solstice approaches, the earth’s tilt slows down considerably. The dominant factor affecting sunrise and sunset is no longer the changing tilt of the Earth, but the difference between our clocks and the position of the sun. That’s why the earliest sunset occurs during this period. After the solstice, the sun begins rising higher in the sky, eventually lengthening the day enough for sunrises to start occurring earlier again in early January.