Every year, a remarkable astronomical event graces our skies — the longest day of the year. While it might not be obvious to everyone, it’s a significant marker in our calendar, bringing with it extended daylight and the official start of summer in the Northern Hemisphere.
But what exactly causes this phenomenon? Let’s dive into the science and traditions behind the summer solstice.
Endless Daylight in the Far North
In parts of the world like Norway, Sweden, and Finland, the longest day of the year isn’t just long — it never ends. Thanks to their high latitude, these regions can experience up to 24 hours of continuous daylight, a natural wonder known as the “Midnight Sun.”
In mainland France and much of Western Europe, the phenomenon is less extreme but still notable. Around the solstice, France enjoys approximately 16 hours of daylight, with only 8 hours of night. So why do our days stretch so long during this period?
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It’s All About Earth’s Tilt
Contrary to what some might think, the increased daylight has nothing to do with Earth being closer to the Sun. Instead, it’s all about the tilt of our planet. Earth spins on an axis tilted roughly 23.5 degrees relative to its orbit around the Sun. As our planet makes its annual trip around the Sun — a journey lasting about 365.26 days — this tilt changes the angle at which sunlight hits different parts of the globe.
During the summer solstice, the Northern Hemisphere is tilted most directly toward the Sun. As a result, sunlight hits us more directly, the Sun climbs higher in the sky at noon, and its path stretches longer across the horizon. This means the Sun rises earlier and sets later, creating the longest day of the year.
Marking the Start of Summer: The Summer Solstice
The summer solstice isn’t just an astronomical event — it’s a cultural one too. Celebrated in various traditions worldwide, the solstice often symbolizes renewal, growth, and light. One of the most iconic celebrations takes place at Stonehenge in the UK, where thousands gather to welcome the sunrise in alignment with the ancient stones.
The solstice typically occurs between June 20 and 21 in the Northern Hemisphere, depending on the year. Thanks to leap years, the exact date can shift slightly. In 2025, the summer solstice will fall on Saturday, June 21, at 4:42 a.m. Paris time, according to the IMCCE (French Institute of Celestial Mechanics and Computation of Ephemerides).
At the same moment, the Southern Hemisphere experiences the opposite — its winter solstice, the shortest day of the year, as it tilts away from the Sun.
The Earth Keeps Turning: What Happens Next?
Once the summer solstice has passed, the days gradually begin to shorten. This isn’t immediately noticeable, but we can lose up to 4 minutes of daylight per day leading up to the winter solstice in December.
The next solstice — the winter solstice — will occur on December 21, 2025. On that day, the Northern Hemisphere will be tilted farthest from the Sun, resulting in the shortest day of the year, with the Sun barely rising above the horizon.
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Between these two extremes — the summer and winter solstices — lie the spring and autumn equinoxes. During these periods, both hemispheres receive equal sunlight, marking moments of balance on Earth.
The Magic of the Midnight Sun
For those living above the Arctic Circle, the solstice season brings a truly magical experience. In the far north, the Sun never sets for several weeks around the summer solstice — a phenomenon known as the Midnight Sun. This rare event paints the sky with soft twilight hues and invites residents and visitors alike to celebrate nature in all its light-filled glory.
Whether you’re experiencing 24 hours of daylight or simply enjoying a long summer evening in your backyard, the summer solstice is a reminder of our planet’s rhythms — and a chance to reconnect with the natural world.