A Moment of Science
What appears to be a dark cloud or haze to our eyes is actually made of millions of tiny particles–in this case, not of water, but of burnt matter. There are two kinds of smoke detectors: ionization alarms and photoelectric alarms.
Now, at sunset, the lowest mile or so of the atmosphere is filled with things like vehicle exhaust, dust, smoke, and water vapor, and all these pollutants scatter light.
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