Eclipse Darkening
Taken by Helio C. Vital on December 14, 2020 @
Saquarema, Rio de Janeiro, Brazil
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Camera Used: Unavailable Unavailable
Exposure Time: Unavailable
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Details:
During the solar eclipse, I used a lux meter (0-20k lux range), whose sensor was facing the ceiling of my verandah, to monitor scattered sunlight. Tens of light intensity readings were made throughout the 2.4-hour long event. Initially at 219 lux, the readings dropped to a minimum of 148 lux at maximum eclipse. They were then corrected for differential atmospheric extinction (<6%). Little interference from intervening cirrus clouds was noticed but deemed acceptable (<4%). In contrast, data gathered during a period of several minutes following mideclipse, when denser clouds significantly blocked sunlight, had to be discarded. In the first figure, the plot for light loss (%) is seen over a photo of maximum eclipse, taken with a Nikon CoolPix P900 camera. Not surprisingly, the light loss measured at maximum eclipse (31.1+-0.7%) and the predicted fraction of the solar disk occulted by the Moon (31.4%) were in agreement. Eclipse maximum occurred at 14:16 (UTC-3h). The lux meter and the camera used are shown in the second photo. Site coordinates were: 22.9263 S and 42.4291 W.
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