The summer solstice is this Friday. Here's what to expect on the 1st day of summer.

This Friday will be the longest day of 2025 in the Northern Hemisphere, kicking off the coveted summer season.

The 2025 summer solstice is expected to officially start on June 20 at 10:42 p.m. ET, according to the Farmers Almanac. It’s at that time that the sun will be at its northernmost point for the Northern Hemisphere. Astronomers recognize the summer solstice as the first day of summer, although it’s not necessarily considered the “official” start of summer.

“The June solstice marks a precise moment in Earth's orbit — a consistent astronomical signpost that humans have observed for millennia,” NASA says. “Ancient structures from Stonehenge to Chichén Itzá were built, in part, to align with the solstices, demonstrating how important these celestial events were to many cultures.”

Thousands of visitors are expected to flock to areas throughout the Northern Hemisphere to celebrate through rituals: from Stonehenge in Wiltshire, England, to midsummer festivals across Sweden, Denmark, Norway and Finland.

Here’s what to know about the summer solstice.

What is the summer solstice?

“Solstice” comes from the Latin words “sol” (meaning sun) and “sistere” (to stand still), according to the Farmers’ Almanac, and it describes the Earth’s angle between the sun’s rays.

The summer solstice is the longest day of the year for the Northern Hemisphere because this is when the Earth’s north pole is tilted toward the sun at its most extreme angle. Solstices only happen twice a year, the second time being when the Northern Hemisphere experiences its winter solstice in December, which is when the Earth’s south pole is tilted toward the sun at its most extreme angle.

On Friday, the Northern Hemisphere will experience its official first days of summer and longest hours of daylight for the entire year. Areas around the equator will experience sunlight for about 12 hours straight, according to Space.com, while more mid-northern areas will get 15 hours. Since the Earth’s north pole is tilted so close to the sun, areas north of the Arctic Circle will experience sunlight for 24 hours.

The summer solstice does not happen at the same time or on the same day every year

The summer solstice can happen anytime between June 20 and June 22, depending on the time zone.

While we measure years in 365 days — or 366 days for a leap year — astronomically speaking, Earth actually takes 365.242199 days to orbit the sun. This affects what time and day the summer solstice will actually occur.

In a lot of Northern Hemisphere locations, areas will experience earlier sunrises before the official solstice day, and some later sunsets happen days after it, according to Time and Date, a global platform that analyzes time zone and astronomy data.

The solstice day never being official or aligned every year is common since the sun’s solar time is never precise or consistent with how our clocks and calendars operate. Astronomers have studied the sun’s timing compared to how we measure time with clocks and calendars, and refer to the difference as “the equation of time.”

What’s the difference between a solstice and an equinox?

Solstices and equinoxes seem to kick off a change in the seasons on Earth, but there are significant differences between the two experiences. Just compare the 2025 spring equinox, which happened on March 20, to what is expected to happen during the upcoming summer solstice on Friday.

Summer and winter solstices are when the Earth’s tilt toward the sun is at its maximum, so the summer solstice is when the Northern Hemisphere experiences its longest day of sunlight and shortest night, and the winter solstice is when the Northern Hemisphere experiences its shortest day of sunlight and longest night.

During an equinox, the Earth is not tilted anywhere directly, and the sun falls right over the equator, which means that there will be “nearly” equal amounts of daylight and darkness at all latitudes, according to the National Weather Service.