When is the summer solstice and what is it?

When is the summer solstice and what is it?

Darren Bett

19 June 2025

• For some it marks a celebration at dawn. For others it is the start of summer and the promise of warmer days to come.

The summer solstice is the longest day of the year, meaning the day with the most hours of daylight.

This year in the Northern Hemisphere, it falls on Saturday 21 June.

And with parts of the UK already experiencing their first heatwave of the year, it’s likely to be a hot one.

Will this be the hottest summer solstice on record?

Forecasters expect temperatures to peak at around 33°C on Saturday, but it is unlikely to be the highest temperature experienced on the day of the summer solstice.

That record was set in 2017 at Heathrow Airport when 34.5°C was recorded.

Typically while this solstice is the day with the most sunlight, the UK’s weather becomes hotter later in the summer when more heat has accumulated in the air and the ground.

Is this the start of summer?

Meteorologically, we are nearly a month into summer. Astronomically, however, the solstice marks the beginning of summer.

When most people refer to the first day of summer, they mean astronomical summer—the summer solstice.

In contrast, meteorologists define summer in the Northern Hemisphere as beginning on 1 June and ending on 31 August.

Meteorological seasons are divided into four three-month periods, which makes it easier to compare seasonal statistics.

Why does the date change?

The solstice always occurs between 20 June and 22, and during a leap year it generally falls on the 20th.

The exact date shifts slightly each year because the calendar year doesn’t perfectly match the time it takes for the Earth to orbit the Sun.

In fact the Earth takes nearly a quarter of a day longer to complete its orbit each year than our calendar accounts for.

This discrepancy is why we add a leap day every four years—to keep the calendar aligned with Earth’s orbit

Why does the amount of sunlight vary?

Our planet does not spin on a perfectly vertical axis—it is tilted.

This tilt causes the amount of sunlight that reaches different regions of Earth to change throughout the year as it orbits the Sun.

For half the year the northern half of the Earth is tilted toward the Sun.

On the summer solstice the Northern Hemisphere is tilted most directly toward the Sun, and the Sun appears directly overhead at the Tropic of Cancer.

Without this tilt, we would still experience weather but not distinct seasons, as the amount of daylight would remain nearly constant throughout the year.

The word solstice comes from the Latin words sol (sun) and sistere (to stand still), referring to the apparent pause in the Sun’s movement across the sky.

How much daylight will there be?

Due to the tilt of the Earth, the period of daylight will be longer at higher latitudes.

Around this time Norway, Finland, Greenland, Alaska, and other polar regions experience ‘midnight sun.’ And across the Arctic Circle, down to a latitude of 23.5 degrees from the North Pole (matching the tilt of the Earth), the Sun does not set at all.

And it may be the longest day, but it is not the latest sunset or the earliest sunrise. The earliest sunrises happen before the summer solstice. And the latest sunsets happen after. Check sunrise and sunset times where you are on the BBC Weather app and website.