Time Of Summer Solstice 2025. This day is also the longest of the year,. Thursday, june 20 is the official first day of northern astronomical summer for 2025 — summer solstice — which is the longest day of the year for this half of the planet.

Usually it’s a decent rule of thumb that seasons start on the 21st of the appropriate month, but that’s not always the case—and this year’s. Edt (2051 gmt), marking the longest day in the northern hemisphere.