How Do You Measure A Sunny Day?

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By By Steve Pool

SEATTLE - In Sept. 3's column, we talked about how Seattle is near the bottom in the U.S. with only an average of 58 sunny days a year. But it's not like a weather observer looks up at noon, sees the sun, and calls it a sunny day.

There are sensors that can actually measure when the sun is indeed shining on it. These sensors will track the number of seconds the sun was shining on it, and divide it by the number of seconds of daylight for that given day.

If the sun shone on the sensor for 70% or more of the day, it's considered a sunny day. If it was between 20-70% of the time, it was a partly cloudy day, and 20% or less, it's a cloudy day.

Your Photos

YouNews Waiting their turn Waiting their turn
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.
YouNews Reflection Reflection
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.
YouNews Weekend Sky Objects Weekend Sky Objects
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
and a Nikon D3100 was used for all the images. Stacking was
done with Deep Sky Stacker (freeware).