The origins of the expression 'Peterburg-gorod belykh nochey' (Saint Petersburg is the city of white nights) are researched to determine whether the twilight phenomenon of June and July known as "white nights," for which the city is famous, is due to atmospheric conditions or only the product of poetic imagination. It is noted that the term 'polyamyy de' (polar day) is used to designate the long summer days in Murmansk, a city located much closer to the Arctic Circle than Saint Petersburg. The broad semantic scope of the Russian adjective 'belyy' (white) is examined to see whether its rich polysemy, literal and figurative meanings, and older usage as a synonym for 'lit' contributed to the metaphor 'belaya noch' (white night). Its occurrence in several poems written in the first half of the 19th century is traced, but Fedor Mikhailovich Dostoevsky's novella 'Belye nochi' (White Nights) (1845) is credited with making the expression popular, although the writer used it as a calque of the French 'nuit blanche' (sleepless night) and not as a designation for Saint Petersburg's summer twilight. (Z. Dubiel in LLBA 2002, vol. 36, n. 5)