What was your longest day

Summer solstice - the longest day and the shortest night of 2021

With the June 21st the astronomical summer begins. Because this date is 2021 for the so-called Summer solstice and the longest day or the shortest night of the year. Reason enough for this astronomical event to have its own contribution to the calendar strange holidays from all over the world and to shed some light on its background with the following lines. What is this date, when the sun reaches its highest point during its annual course?

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What is the summer solstice?

Solstices or solstices (lat. Solstitium - dt. Standstill of the sun) denote an astronomical phenomenon in which the sun reaches the greatest north or south distance from the celestial equator of the earth in the course of the year.

With this in mind, the summer solstice on June 20, 21 or 22 marks the beginning of the astronomical summer. Because on this date the sun reaches its highest position in the meridian passage regardless of time zones and coordinates. This means that the solstice takes place everywhere at the same time in both winter and summer. In the case of the June solstice, it should also be noted that the distance between the sun and earth during the sixth month of the year is actually about five million kilometers greater than at the time of the winter solstice on December 21 or 22

Since the majority of the daily solar path lies above the horizon from the earth's perspective, the summer solstice stands for the longest day or the shortest night of the year. In short, there is no longer any other day of the year. This phenomenon can be observed particularly clearly at the Arctic Circle, where no sunset occurs during the summer solstice. In the context of this so-called midnight sun or white nights, the sun's path lies completely above the horizon line and it does not get dark.

Interesting side note: In fact, this phenomenon can also be observed south of the Arctic Circle. Depending on the respective weather conditions (air pressure and temperature), the sun's rays are deflected by the earth's atmosphere in such a way that the sun remains visible below the horizon and thus there is hardly any darkness up to 100 kilometers away beyond the Arctic Circle.

Summer solstice: When is the longest day or the shortest night of the year?

While in the 20th century the summer solstice in the Central European time zone could also fall on June 22nd - most recently in 1986 - the event has been spread relatively constantly on June 21st since the beginning of the 2000s. Only from 2020 does this astronomical constellation of earth and sun fall again on June 20. The reason for the calendar shift, as already indicated above, is the leap year rule (365.2425 days), which corrects the actual length of the year (365.2422 days).

So that nobody has to complain that he / she did not know anything about it, the following is an overview of the exact dates for the longest day or the shortest night of the year including the respective day of the week and the specific CET time of the highest Point of the sun position:

  • 2018: Thursday, June 21st - 12:07 pm CEST
  • 2019: Friday, June 21st - 5:54 pm CEST
  • 2020: Saturday, June 20th - 11:43 pm CEST
  • 2021: Monday, June 21 - 05:32 CEST
  • 2022: Tuesday, June 21st - 11:13 am CEST
  • 2023: Wednesday, June 21st - 4:57 pm CEST
  • 2024: Thursday, June 20th - 10:50 PM CEST
  • 2025: Saturday, June 21st - 4:42 am CEST
  • 2026: Sunday, June 21st - 10:24 am CEST
  • 2027: Monday, June 21 - 16:10 CEST
  • 2028: Tuesday, June 20th - 10:01 pm CEST
  • 2029: Thursday, June 21st - 3:48 am CEST

The calendar of curious public holidays from all over the world also includes a whole series of summer events and days of action, which are thematically linked to the respective date of the June solstice. Here are, among other things, World Dachshund Day on the June solstice, World Giraffe Day and US Shell Day (National Seashell Day) or International Surfing Day and International T-Shirt Day.

Calendar Knowledge: Five Curious Summer Solstice Facts You Should Know

Even if the previous statements about the astronomical phenomenon of the summer solstice are based on empirical observation or mathematical calculation, there are also a number of interesting facts that should not necessarily belong to general education in this form. The following aspects can be reported:

  • The longest day of the year does not cover the same amount of time everywhere. Because the closer a place is to the Arctic Circle, the longer the days around the summer solstice are. This means that Flensburg has a longer daylight phase here than, for example, in Geneva or Zurich.
  • From the point of view of weather observation and temperature measurement, the astronomical beginning of summer is by no means to be equated with the warmest time of the year. Because on the statistical average, the months of July and August are significantly warmer than June. This phenomenon is due to the slow warming and the surplus of energy that is created in the atmosphere by solar radiation.
  • While astronomers and meteorologists have very different views of the beginning of summer, our Scandinavian neighbors see the matter much more pragmatically and simply celebrate the summer solstice as the middle or high point of summer. After all, it just doesn't stay light longer than on this date (see also the article on St. John's Day on June 24th).
  • But here, too, the old wisdom applies: where there is a lot of light, there is also a lot of shadow. Because with the summer solstice, the days become constantly shorter again as the earth moves further and the northern hemisphere moves away from the sun again until the winter solstice in December.
  • In addition, the longest day of the year is not to be equated with the latest sunset or the earliest sunrise. The combination of the inclination angle of the earth's axis and the elliptical shape of the earth's orbit around the sun is responsible for this phenomenon. Due to this fact, the position of the sun shifts daily and the mother star of the earth moves across the sky at an irregular speed. In the case of the June solstice, the course of the sun slows down and accordingly the earliest sunrise or sunset of the year is ten days before or after the respective solstice. This difference between true solar time and mean local time is also known as the equation of time.

With that in mind: Hurray for the summer solstice, long days and short nights. At least here in the northern hemisphere. And there is also a positive message for our fellow human beings in the southern hemisphere. As of today, the days are definitely getting longer again. :)

More information and resources on the June solstice

Categories Astronomical Curiosities, Flexible Holidays, June, Meteorological HolidaysTags June 21st