When Is The Longest Day Of The Year 2024. The longest day in united kingdom is 24 hours long i.e. In the southern hemisphere, it will occur on december 21, 2024.

The solstice is celebrated twice a year for summer and winter or the longest and shortest daylight during the year. Thursday, june 20 is the official first day of northern astronomical summer for 2024 — summer solstice — which is the longest day of the year for this half of the planet.