(NewsNation) — The summer solstice, falling on June 20, 2024, will be the earliest solstice in more than 200 years, thanks to a quirk in the Gregorian calendar.

The solstice will be the earliest since George Washington was president, the French Revolution was in full swing and Jane Austen began writing “Pride and Prejudice.”

What is the summer solstice?

The summer solstice occurs when the Earth reaches maximum tilt toward the sun. For the northern hemisphere, the 2024 summer solstice falls on June 20 at 4:54 p.m. ET.

While it’s often referred to as the longest day, the solstice is more precisely the most daylight, as all days have 24 hours. The exact amount of daylight depends on latitude, with extreme northern locations experiencing the midnight sun, where the sun never fully sets.

The amount of daylight will remain roughly steady for a few days before it slowly begins to decrease until the winter solstice, which marks the fewest hours of daylight of the year.

What does the solstice mean?

The solstice also marks the start of astronomical summer. If the current heatwave has you feeling like summer is already here, that’s because meteorological summer, which marks the three hottest months of the year, began at the start of June.

The solstice is something that has been observed by humans since ancient times, with monuments like Stonehenge having been built to align with the sun on the summer and winter solstices.

Even today, hundreds of people will gather at sites like Stonehenge to observe the day. In other places, the solstice is celebrated with bonfires and festivals like Sweden’s Midsommar.

Why is this solstice so early?

The reason this year’s solstice is the earliest since 1796 is because of the way the calendar is designed. The Earth doesn’t orbit the sun in precisely 365 days, so the Gregorian calendar adds leap years every four years, inserting an extra day in the calendar to keep things on track.

But there’s a quirk in how leap years are calculated. Years that begin with 00 are only leap years if the year is also divisible by 400. Over the course of 400 years, that means the planet loses three leap years, shifting time slightly and making things too fast by about 45 minutes.

That means the solstice this year is about 45 minutes earlier than previous years. It’s a trend that will continue until 2096, the solstice creeping earlier with each orbit around the sun until the calendar resets.