the period of time centered upon the summer solstice, and more specifically the northern European celebrations that accompany the actual solstice or take place on a day between June 19 and June 25 and the preceding evening. The exact dates vary between different cultures. The undivided Christian Church designated June 24 as the feast day of the early Christian martyr St John the Baptist, and the observance of St John's Day begins the evening before, known as St John's Eve.
These are commemorated by many Christian denominations, such as the Roman Catholic Church, Lutheran Churches, and Anglican Communion. In Sweden the Midsummer is such an important festivity that there have been serious discussions to make the Midsummer's Eve into the National Day of Sweden, instead of June 6. It may also be referred to as St. Hans Day.
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The date had stuck in Winston’s memory because it chanced to be midsummer day; but the whole story must be on record in countless other places as well.
George Orwell. 1984 (1949)
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Salander got out her Kawasaki on Midsummer Eve and spent the day giving it a good overhaul.
Stieg Larsson. The Girl with the Dragon Tattoo (Reg Keeland translation), p.386 (2009)