A reality based independent journal of observation & analysis, serving the Flathead Valley & Montana since 2006. © James Conner.

23 August 2017 — 1314 mdt

Flathead Memo commits eighth grade science,
measures intensity of sunlight during the eclipse


While President Trump was staring at the sun with his unprotected orbs, I was watching an image (right) of the eclipse projected through a pinhole — and using my 45-year-old Weston Master 6 light meter, which reads out in candles per square foot, to measure the intensity of the sunlight every few minutes.

My NASA designed, homebuilt, pinhole projection viewer, made from a cereal box, duct tape, and aluminum foil (Teflon coated, a slick touch), is at right. A sheet of white paper is glued to the bottom inside. A ten-cent apparatus that provided a ten-dollar view.

I measured the illumination from the sun, incident light in photographic lingo, rather than the light reflected from a gray card. The reading is the same, but measuring incident light, a standard technique in cinematography, is easier and gives more consistent results.

At the eclipse’s maximum, the sunlight was one-tenth as intense as when the sun was uncovered. That indicates the moon covered 90 percent of the sun, which was the prediction for Kalispell. I did not expect my measurements to yield such close agreement with the prediction; Lady Luck was my lab assistant.


Here are my data:

Time Candles/ft^2
11:14:00 125
11:20:00 100
11:29:00 64
11:38:00 80
11:50:00 200
12:10:00 350
12:30:00 500
12:40:00 650