Lebo was watching the night sky on a clear evening in November. He noticed that sometimes when he looked directly overhead he could detect a very faint star. A few minutes later it seemed that the star had disappeared, and then it "appeared" again. In this case, it is very likely that the light from the star was

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The fact that Lebo was sometimes able to detect the faint star and sometimes not suggests that the light from the star was hovering around his absolute threshold for light perception. This means that the light was at the minimum level required for Lebo to detect it, and sometimes it may have become too weak to cross that threshold, causing the star to disappear momentarily before becoming visible again.

Lebo Was Watching the Night Sky on a Clear Evening