When is the summer solstice and how hot will the weather be?

Sunday marks the summer solstice, marking the official start of astronomical summer across the northern hemisphere.

We generally think of it as a whole day - with the longest time of daylight and the shortest period of nocturnal darkness - but the solstice actually happens at an exact time.

This year it is at 09:24 BST on 21 June - this moment the northern hemisphere is most tilted towards the Sun.

The weather for those marking the solstice is expected to be largely dry, mostly sunny, and hot in the south where temperatures could soar above 30C (86F).

As the Earth orbits the sun over a year, it spins on a tilted axis, fixed at 23.4 degrees.

It is this tilt that causes the amount of sunlight that reaches different parts of Earth to change throughout the year.

In the summer the northern hemisphere is tilted towards the Sun and experiences its longest days.

At the summer solstice the northern hemisphere is tilted most directly toward the Sun, and the Sun appears exactly overhead at the Tropic of Cancer.

The solstice does not always fall on the 21 June. Depending on the year, it can also take place on 20 June or 22 June too.

In a leap year, it generally falls on 20 June.

This variation is because it actually takes the Earth almost six hours longer to orbit the Sun than the length of a full calendar year.

To keep the calendar aligned with the Earth's orbit an additional leap day is added in every four years to make up for this difference.

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.

Despite being the longest day of the year, the summer solstice does not have the latest sunset or the earliest sunrise.

The earliest sunrises happen before the summer solstice and the latest sunsets happen after.

You can check sunrise and sunset times where you are on the BBC Weather app and website.

Stonehenge is a world-famous prehistoric monument completed in the late Neolithic period in about 2500 BC.

The exact purpose of the stone circle is unknown.

But as the stones line up precisely with the rising Sun for both the summer and winter solstices this "suggests that it was a prehistoric temple aligned with the sun's movements" according to English Heritage.

Throughout history, Stonehenge has been - and continues to be - an important site for worshippers to conduct rituals and ceremonies relating to the changing seasons, the sun, and the sky.

Most places will stay dry with plenty of sunshine on Sunday.

It will be a hot day, especially in the south, where temperatures are likely to reach around 26 to 31C (79 to 88F). The northern half of the UK will be a little less hot at 15 to 25C (59 to 77F).

But as heat and humidity rise, there is a threat of some isolated thunderstorms, especially for eastern England.

While the solstice marks the beginning of astronomical summer, for meteorologists it started several weeks ago.

Meteorologists define summer in the northern hemisphere as beginning on 1 June and ending on 31 August.

This is because all four seasons are divided into specific three month periods in order to make it easier to compare seasonal statistics.