White nights

Poetical name of the phenomenon of northern widths connected with rotation of the earth and increase of light day in summer months. Apogee is day of a summer solstice on 22nd of June, when night the shortest in a year. In St.-Petersburg the phenomenon not on is bright, as behind Polar circle so much, but the word combination is connected with this city"White nights". It some kind of one of the city cards, distinguishing northern capital from other cities of the world.