The longest day of the year is not fixed, but alternates between two specific dates each year.
The longest day of the year, also called summer solstice, is the day of the year when the sun passes the highest point in its path across the sky.
This means that the hours from sunrise to sunset are more than any other day during the year as the northern end of the Earth’s axis of rotation slopes directly towards the Sun.
The date varies due to the difference between a calendar year and a solar year, but is corrected approximately every four years when there is a shooting year.
In recent years, summer solstice has fallen 21 June and in 2018 and 2019, the longest day of the year will also fall on this date.
Only in 2020 the longest day of the year will be 20 June.
The exact time when summer solstice occurs, however, vary year by year.
21st June also naturally marks the transition to gradually shorter days, which continues to diminish in the long term until winter solstice – the shortest day of the year, correspondingly always falling either on 21 or 22 December.
The night after summer solstice is by far the shortest night of the year, as the bright hours are so full.