Summer is the warmest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice. The date of the beginning of summer varies according to climate, tradition and culture, but when it is summer in the Northern Hemisphere it is winter in the Southern Hemisphere, and vice versa.
It is also used by many in the United Kingdom. In Ireland, the summer months according to the national meteorological service, Met Éireann, are June, July and August. However, according to the Irish Calendar summer begins on 1 May and ends on 1 August. School textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June.