Hour

Hour, a measure of time equal to $\backslash frac\{1\}\{72\}$th part of an astronomical day or to $\backslash frac\{1\}\{12\}$th part of a natural day (excluding the hours of night or darkness). See DAY, and TIME; and for the hours in Catholic usage, see BREVIARY.—Hour-circles, in astronomy, are any great circles which cut the poles.