What is the thinnest crescent Moon visible to the unaided eye during daylight? A good question, to which I do not have an answer, though I do have an observation.
Seeking the thinnest crescent Moon during evening or morning twilight without optical aid has long been a fun and challenging pursuit among amateur astronomers. As early as 1921, Popular Astronomy asked amateur astronomers to “take up the matter, in order to determine how frequently it may be detected when less than 24 hours.” But I have not encountered any studies on how thin of a crescent the eye can detect with the Sun in the sky.
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