People living in the Northern Hemisphere are set to witness the longest day of the year as the June solstice marks the official start of summer. Depending on where you are in the world, this annual event happens on either June 20 or June 21.

What is the summer solstice?

Known as the June solstice, this event begins summer's arrival in the Northern Hemisphere and winter's beginning in the Southern Hemisphere. It brings early sunrises, late sunsets, shorter nights, and more daylight hours than any other day of the year for the Northern Hemisphere.

On this day, the sun reaches its highest point in the sky, bathing parts of the world in sunlight for the longest stretch of the year.

The science behind the solstice

The summer solstice happens because of the way Earth tilts on its axis. Earth is tilted at about 23.5 degrees compared to its path around the Sun. As NASA explains, this tilt is what causes the seasons.

During the June solstice, the Northern Hemisphere is tilted most directly toward the Sun, receiving more direct sunlight. This results in longer days and warmer weather. At the same time, countries in the Southern Hemisphere, such as Australia, South Africa, and New Zealand, experience their shortest day, marking the beginning of winter there.

For many cultures around the world, the summer solstice holds deep traditional, religious, and agricultural significance.

It has helped shape rituals and seasonal festivals, guided farming decisions such as when to plant or harvest, and even influenced how ancient calendars were created.

When will the summer solstice happen in 2025?

Mark your calendars! In 2025, the summer solstice will occur at 2:42 UTC on June 21, which is 10:42 p.m. EDT on June 20.