What does the beginning of autumn mean for sunrise and sunset times?

PHOENIX (AZFamily) – Autumn, also known as the fall equinox, begins this Sunday (September 22, 2024) at 5:43 a.m. Arizona time.

For fall to officially begin, the Earth's tilt must be just right. The start of fall is marked by the moment when the Earth is tilted so that the sun is directly over the equator.

In contrast, during the summer solstice, the Earth is tilted so that the sun's rays are directed toward the Tropic of Capricorn. Arizona is in the Northern Hemisphere, so we have more daylight in the summer.

The following graphic shows an illustration of the autumn equinox.

You can also see above that “equinox” is Latin for “equal nights.” In fact, the equinox is a time when day and night are almost equal in length, but they are not exactly equal in length. Notice that on the first day of fall, this Sunday, there are a few more minutes of daylight than darkness.

Why are day and night not exactly the same length on the first day of fall? One of the main reasons is “refraction,” the way the sun's rays are refracted by the sun. This refraction makes sunlight appear even when the sun is technically below the horizon.

The graph above also shows the difference between sunrise and sunset on the first day of fall compared to the last day of fall. Daylight duration changes from about 12 hours and 7 minutes on the first day of fall to about 9 hours and 56 minutes on the last day. That's a reduction of over 2 hours in about three months!

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