What angular span, measured by a fully stretched hand at arm's length, can help an observer estimate the $22^ ext{o}$ halo?
Answer
Roughly $20^ ext{o}$ to $25^ ext{o}$
To help observers gauge the large scale of the $22^ ext{o}$ halo, a simple method involves using the human hand held fully extended at arm's length. When held this way, the span stretching from the tip of the little finger across to the tip of the thumb typically covers an arc of approximately $20^ ext{o}$ to $25^ ext{o}$. If an observer can center the Moon within this hand span, they can confirm that the ring they are observing is indeed the telltale $22^ ext{o}$ halo, providing immediate context for the size of the atmospheric optics involved.
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