After the meteorological beginning of summer on June 1 and the even earlier phenological beginning of summer, summer also begins today at exactly 4:57 p.m. in calendar or astronomical terms. One speaks also of the summer solstice, the sun stands vertically over the northern tropic. This is associated with the longest day and the shortest night in the northern hemisphere, from now on the length of the day decreases again.
Already summery for a while, but on the calendar only as of today
In June so far and partly already in May summery and recently even midsummery conditions have set in, even if calendrically it was still spring. Today, June 21, is the official start of summer in Switzerland. That means that the sun over the northern hemisphere has the highest noon position above the horizon and the sun is exactly at 16 o'clock 57 Central European Time vertically over the northern tropic. Thus there is today to the so-called summer solstice the longest day and the shortest night of the year, and it begins calendrical and/or astronomically the summer. The summer lasts thereafter to 23 September, where at 8 o'clock 49 the sun stands vertically over the equator and thus calendrical the autumn begins.
The following graphic shows schematically the situation of earth and sun at today's summer solstice.
Fig. 1: Astronomical constellation at today's summer solstice; Source: MeteoNews
Basically, the seasons are caused by the fact that the Earth does not orbit the Sun at right angles to its orbit, but that the Earth's axis is inclined by about 23.45 degrees.
By the way, the day of the astronomical beginning of summer varies, because according to the calendar a year lasts 365 days, but the astronomical year lasts 365 days, 5 hours and 49 minutes. To compensate for the difference, there is a leap year every four years.
Summer solstice festivals and customs
The summer solstice gives rise to major festivals and customs in some countries. These include, for example, the solstice celebrations at Stonehenge, the Golowan festival in Cornwall, the various St. John's bonfires and, above all, the Midsummer festival in the Scandinavian countries. Since pagan times, the day has been regarded in popular belief as shrouded in legend and shrouded in mystery. The numerous defensive spells against witches and demons then gradually developed into cheerful folk festivals.
Fig. 2: Solstice fires are common in different countries; Source: pixabay
More summer beginnings
In addition to today's calendar or astronomical beginning of summer, there are also meteorological and phenological beginnings of summer. More about this here.