What does the start of fall mean for sunrise and sunset times?

PHOENIX (AZFamily) — Fall, otherwise known as the autumnal equinox, starts at 5:43 a.m. Arizona time this Sunday (Sept. 22, 2024).

The earth’s tilt has to be lined up just right to officially start autumn. The beginning of autumn is marked by the moment the earth is tilted so that the sun is directly over the equator.

By contrast, during the summer solstice, the earth is tilted so that the sun’s rays are directed at the Tropic of Cancer in the northern hemisphere. Arizona is located in the northern hemisphere, so we get more daylight in the summer.

The graphic below shows an illustration of the autumnal equinox.

Above, you will also see that “equinox” is Latin for “equal nights.” Indeed, the equinox is a time with nearly equal amounts of day and night, but it’s not exactly equal. Notice that on the first day of fall this Sunday, there are a few more minutes of daylight than darkness.

So why is the day and night not exactly equal on the first day of autumn? One of the main reasons is “refraction,” or the way that the sun’s rays are bent by the sun. This refraction allows sunlight to appear even if, technically, the sun is below the horizon.

The graphic above also shows the difference between sunrise and sunset on the first day of autumn versus the last day of autumn. The daylight changes from about 12 hours and 7 minutes on the first day of autumn to about 9 hours and 56 minutes on the last day. That’s a decrease of over 2 hours in about three months!

Impact on driving

Do you ever wonder why it’s so hard to see when driving around sunrise and sunset this time of year? Blame it on early city planners in the late 1880s and the changing seasons.

The city of Phoenix was founded in 1881, and its streets were laid out in what is commonly called a grid pattern.

This means that most streets intersect at 90-degree angles.

So during the spring and fall equinoxes, when the sun is rising and setting due east and west, the sun lines up with those roads that stretch across the Valley.

The rising and setting sun is shining directly into your front windshield, making it difficult to see in the first few hours of sunrise and sunset.

That’s why it’s so important to wear your sunglasses and flip your vehicle’s sun visor down when driving east and west this time of year. The fall equinox is this Sunday, so safe driving!

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