Hello, summer! June solstice brings the start of summer, and the longest day of the year, to North America

Update: Summer officially begins tonight in North America! Read on to find out exactly when and why.

Each year on the summer solstice, revelers at Stonehenge in England stay up all night to celebrate the dawn of the longest day of the year in the Northern Hemisphere, with many images streamed live.

But this year, there's a twist: The summer solstice there will occur on a different day than the solstice in North America, due to time zone differences. So when is the summer solstice in 2025, and what's the science behind it?

This year, the summer solstice in the Northern Hemisphere occurs at 02:42 UTC on Saturday, June 21, 2025. That means it's at 10:42 p.m. EDT on Friday, June 20 and at 3:41 a.m. BST on Saturday, June 21.

The event’s name is instructive: "Sol" means "sun" in Latin, while "stice" means to stand still. That's exactly what appears to happen on two days each year — one between Dec. 20 and Dec. 22, and the other between June 20 and June 22 — when the sun rises and sets at its most northerly or southerly points on the horizon.

If you consider the seasons and the sun's position in the sky, that checks out: The sun reaches its highest point in the midday sky in the Northern Hemisphere on the day of the summer solstice, which means it must be rising at its farthest northeast and setting at its farthest northwest.

Precisely the opposite is happening in the Southern Hemisphere, where the June solstice is the winter solstice. When the sun is highest in the Northern Hemisphere's daytime sky, it's the lowest in the Southern Hemisphere's daytime sky. The situation is reversed for the December solstice, the longest day and the shortest night in the Southern Hemisphere. At the equinoxes ("equi" and "nox," meaning equal night), between March 19 and 21 and between Sept. 21 and 24, the sun appears to rise and set due east and west, respectively, from everywhere on Earth.

Related: The 10 best stargazing events of 2025

Solstices and equinoxes happen because Earth's axis of rotation is tilted 23.5 degrees from the plane of its orbit around the sun, which causes the seasons. On the summer solstice, the Northern Hemisphere is tilted toward the sun, so it receives the full glare of the sun's rays for the longest time and the day is therefore the longest.

Following this logic, it would seem that the summer solstice should also be the warmest day of the year. However, there's a slight seasonal lag because our mostly watery planet takes time to absorb the heat, according to the Royal Meteorological Society. At the North Pole, the sun does not set on the summer solstice, while at the South Pole, the sun does not rise.

Editor's note: This article was updated on June 20 to mark the beginning of the summer solstice in North America.