During the summer solstice, the day is the longest of the year while the winter solstice marks the longest night of the year but the dates of the winter and summer solstices are reversed for the hemispheres North and South.
The summer solstice is the date of the longest day of the year (and therefore the shortest night) in a hemisphere: northern hemisphere in June, southern hemisphere in December.
The dates of the equinoxes can be calculated on the IMCCE website. For example, the date of the summer solstice in the Northern Hemisphere in 2006 is June 21 at 12h 26min UTC. But the solstices (as well as the equinoxes) are astronomical phenomena independent of the observers and it is interesting to notice, expressed in UTC or UT hours to remain universal, the variations of the date of the solstices in the calendar year since the creation of the calendar Gregorian (1582). This variation is caused by the difference in duration between the calendar year (365 or 366 days) and the tropical year (approximately 365.2422 days).
The summer solstice corresponds to the beginning of the summer and is often the occasion of festivals: the fires of Saint Jean Baptiste for the Christians but also the festival of the music for some years.
The four seasons (views from across the Rhine ...). Äquinoktiallinie = line of equinoxes, Solstitiallinie = line of sostices.
The winter solstice is the date of the shortest day of the year (and therefore the longest night) in a hemisphere: northern hemisphere in December, southern hemisphere in June.
Since the creation of the Gregorian calendar (1582), the winter solstice in the northern hemisphere falls on the 20th, 21st, 22nd or 23rd of December. It usually falls on December 21st or 22nd. It fell on December 23rd in 1903 and it will be necessary to wait until the beginning of the 24th century to see it falling again on this date. It fell on December 20 10 times in the late 17th century and will fall again on this date at the end of the 21st century and at the end of .... 25th century.
The winter solstice marks, in a number of cultures, the first day of winter and is usually associated with a holiday, such as the Roman Saturnalia, Hanukkah in the Jewish religion, Kwanzaa for some African-Americans or Christmas, ancient pagan festival assimilated by the Christian religion.