First Day Of Summer 2024 Uk. The longest day of summer is the summer solstice, which marks the first day of astronomical summer. The solstice this year falls on thursday june 20 2024, which will officially be the longest day of the year.
In 2024, summer solstice in the northern hemisphere will occur on thursday, june 20 around 4:50 p.m. June 21st, 2024 is the official start date of the summer.