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In page Atmospheric refraction:

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Day-to-day variations in the weather will affect the exact times of sunrise and sunset[6] as well as moon-rise and moon-set, and for that reason it generally is not meaningful to give rise and set times to greater precision than the nearest minute.[7] More precise calculations can be useful for determining day-to-day changes in rise and set times that would occur with the standard value for refraction[note 1] if it is understood that actual changes may differ because of unpredictable variations in refraction.