The longest day of the year in the Northern Hemisphere is approaching: when is it and why does it happen?

On June 21, 2025, the Northern Hemisphere will experience the longest day of the year, better known as the 'summer solstice.' This astronomical phenomenon marks the official start of summer and occurs because the Earth's axis is at its maximum tilt toward the Sun , generating the greatest number of hours of sunlight in a single day.

During this event, daylight hours vary depending on the latitude. In some cities, such as Bogotá, located near the equator, the difference in daylight hours is very minimal throughout the year. However, in more northern regions, such as Europe and North America, the phenomenon results in up to 16 hours of daylight.

This event is significant not only for the extension of daylight hours, but also for its cultural and social impact. Many cultures around the world celebrate festivals and rituals in honor of the summer solstice, recognizing its importance in agriculture and daily life.

This phenomenon occurs due to the tilt of the Earth's axis, which is 23.5 degrees, which causes some areas of the planet to receive different amounts of sunlight throughout the year.

"The moment when one of the Earth's hemispheres reaches its maximum tilt toward the Sun is called the summer solstice in that hemisphere. On this day, it receives the most sunlight, resulting in the longest day of the year there," explains the StarWalk portal.

On June 21, the North Pole will be tilted completely toward the Sun, placing the great star at its highest point in the sky at noon for the Northern Hemisphere, paving the way for this astronomical event.

It's important to note that although this day will have the most daylight hours, it's not necessarily the day with the highest temperatures of the year. This is because the oceans and atmosphere take longer to warm up, causing a delay in peak temperatures until July or August in different parts of the world.

For those who want to make the most of this day, it's a great opportunity to engage in outdoor activities, such as hiking, picnicking, or simply enjoying the lingering sunset.

Meanwhile, in the Southern Hemisphere, the seasons are reversed. There, summer will begin on December 21, 2025, so astronomers prefer to refer to the June or December solstice to avoid confusion.

According to StarWalk, the days begin to shorten just after the summer solstice. This is the day when people experience the most daylight, and then the days become shorter. By the autumn equinox, the length of day and night are nearly equal .

Locations closer to the poles experience greater differences in day length throughout the year, so summer days are longer there. In Whitehorse, Canada, which is far north, the longest day in 2025 will be 19 hours and 9 minutes. In Bogotá, Colombia, near the equator, the longest day will last 12 hours and 23 minutes, according to the specialized portal.

Places within the polar circles experience midnight sun or polar day for a few days or months when the sun does not set at all.