Why Aren't The Sunrise And Sunset Equal On The Equinox?

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By By Steve Pool

SEATTLE - The first days of spring and fall are a time when there is equal 12-hour daylight across the planet. However, looking at a Seattle sunset chart shows Seattle has 12 hours and 11 minutes of daylight on Sept. 21. Why?

Sunrise and sunset are calculated when the top of the sun is on the horizon. However, equal daylight is measured from the center of the sun -- accounting for a few minutes. The other discrepancy is from when the sun is on the horizon, the Earth's atmosphere bends the sun's light.

As a result, the sun still looks to be above the horizon for a few minutes after it has already set. The U.S. Naval Observatory takes this into consideration when calculating sunrise and sunset times.

For More Information -- www.usatoday.com

Your Photos

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A Washington State Ferry waits its turn to dock at the Lopez Island Ferry Terminal as the sun rises over Mount Baker in the background.
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During my time in Seattle, WA, I've had the opportunity to take all sorts of interesting pictures. There is water everywhere here, and in this shot; it provides a perfect mirror to the road above.
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These images were taken Friday and Saturday under with a bright moon. M42 is a 45 minute stack of 122 frames and M15 is a 34 minute stack of 14 frames. A Meade 6-inch refractor
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