Second summer

A period of abnormally warm weather that occurs in mid- to late autumn and after the first frost.

The comparable period in Europe is termed the Old Wives' summer and, poetically, may be referred to as halcyon days. In England, dependent upon dates of occurrence, such a period may be called St. Martin's summer, St. Luke's summer, and formerly All-hallown summer.

Term edited 25 October 2020.

Any function of time f(t) is periodic with period t if f(t) = f(t + τ) for all times t, where τ is the smallest number for which this equality holds.