What precise minimum angle reflects light refraction by common hexagonal ice crystals in a lunar halo?
Answer
$22^ ext{o}$
The 22-degree halo is the most striking and common form observed around the Moon. This specific measurement, $22^ ext{o}$, is not arbitrary; it precisely represents the minimum angle at which light is refracted by the standard hexagonal ice crystals present in the atmosphere. Although measurements can sometimes range slightly lower, such as between $21.5^ ext{o}$ and $21.8^ ext{o}$, the $22^ ext{o}$ figure is the universally accepted standard used to describe this pervasive optical event, signifying the predictable path light takes through these specific atmospheric prisms.
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Related Questions
What optical phenomenon causes the luminous ring known as a lunar halo?What precise minimum angle reflects light refraction by common hexagonal ice crystals in a lunar halo?Which specific types of high-level clouds produce the ice crystals necessary for a lunar halo?Approximately how many times the Moon's diameter must be stacked to span the $22^ ext{o}$ circle outward to the ring?What inherent geometric property of ice dictates the $22^ ext{o}$ minimum deviation angle for the halo?In mid-latitude areas, what weather condition often follows the appearance of a high-level lunar halo?For the $22^ ext{o}$ halo to form, what specific angle must the exit face be relative to the entry face of the hexagonal ice crystal?What observation suggests turbulence within the high cloud layer when viewing a lunar halo?Besides the $22^ ext{o}$ halo, what other, larger halo is sometimes produced by moonlight interacting with ice crystals?What angular span, measured by a fully stretched hand at arm's length, can help an observer estimate the $22^ ext{o}$ halo?