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Why Don’t Sunrise and Sunset Times Change by the Same Amount Each Day?

-- Dave Fox | February 9, 2020

Question:

I just saw a chart detailing the official sunset/sunrise times in my locality (Tucson, AZ) for the month of January. I noticed that sunset times became later by 27 minutes from 1/1 through 1/31, whereas sunrise times became earlier by just 6 minutes over the same period of time. It struck me as odd that those two numbers would be different. Why?

-- Dave Fox

Answer:

This is due to two things. The Earth’s orbit around the Sun is elliptical, rather than circular, and the Earth’s axis of rotation is not perpendicular to the plane of the orbit. This non-circularity of the orbit and the tilt of the Earth’s axis of rotation both contribute to the uneven changes in the times of sunrise and sunset. For example, as you noticed, the Sun rises only a little earlier each day in January, but sets noticeably later each day. Let me point you to a more detailed answer on the Quora blog if you would like to dig a bit deeper into this subject.

-- Jeff Mangum

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