The first day of summer in 2025, based on the astronomical definition, is Friday, June 20, 2025, at 10:42 p.m. EDT. This is the moment of the summer solstice, when the Sun reaches its northernmost point relative to the equator, marking the official start of summer in the Northern Hemisphere. However, some definitions like the meteorological summer consider June 1 as the start of summer, which lasts until August 31. For astronomical purposes, summer will end on Monday, September 22, 2025, with the autumnal equinox.
Note also that the exact date and time of the solstice can vary slightly depending on local time zones. For example, in the UK, the solstice is noted as occurring on Saturday, June 21, 2025, at 03:42 BST.
