Interesting definition, i never thought about it in this way. It seems that in Scandinavia the celebrate June 23rd as Midsummer. <a href=http://www.ingebretsens.com/archive/scan_midsummer/archive_scan_midsummer.htm">Here they write:

<quote>Midsummer, an observation of the longest day of the year, is celebrated in each of the Scandinavian countries. Midsummer, originally a pagan holiday, is celebrated on the day of John the Baptist and is now held on the weekend closest to the summer solstice.</quote>

But which date Shakespeare meant, i don't know.