The Darkening

This is the second of two experiments I tried during the April 8 solar eclipse. In Arizona the eclipse was around 65% partial. A 35% reduction in ambient light is not easily perceived by the human eye, because as the light level decreases, the retina’s rods start kicking in to compensate for the less efficient cones — a process known as dark adaptation.

But I wanted to see if a camera could detect it. So I set my Canon 20D (with the standard 18-55 mm zoom lens) to full manual. That prevents the camera from automatically compensating for changing light levels. In Arizona, first contact was 10:08 am MST and last contact was 12:35 pm MST with maximum coverage at 11:20 am MST. At 9:50 am I took several shots and determined the settings should be: f/29, 1/25 sec, ISO 400. That provided a good exposure of the bird feeder in my front yard, the landscape around it, and some distant hills.

The video begins at 10:00 am and ends at 1:00 pm, so with three hours compressed into a 1 minute video the speedup factor is 180X. Even with the fixed camera settings it’s difficult for the eye to notice any change in the ambient lighting. There were some clouds drifting in the sky and you’ll see their effect on the background hills. To see the effect of the eclipse, I suggest you pause the video at the 27 seconds (maximum coverage), and then click back to the start (or ahead to the end). You will easily see the change in ambient lighting.

Interestingly, 27 seconds is when activity at the bird feeder picks up. They don’t feed much during the day and prefer early morning or late afternoon. You can see them feeding in the video but the birds flash in and out rapidly at 180X. You’ll see mostly quails and finches, and maybe a couple of doves. The reaction of wildlife to eclipses is well-documented.

So I’d consider this eclipse experiment a success — the previous one less so. That’s the really cool thing about science. Sometimes you find what you’re seeking, sometimes you find what you’re not seeking, and sometimes you find nothing and have to revise your experiment. But you always learn.

Next Week in Sky Lights ⇒ Small Modular Reactors

April 8 Solar Eclipse
Small Modular Reactors
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