In 2024, June 20 marks the summer solstice, the first official day of astronomical summer.
“Solstice” means the sun has gotten as high in the sky as it’s going to get for the year; on Thursday, that will happen at 4:51 p.m. Eastern Daylight Time.
For those looking to pass the time during those extra hours of natural sunlight for reading, below TIME rounds up some surprising facts about the summer solstice and its history.
The summer solstice is the longest day of the year
In New York City, for example, the sun will rise on Thursday at 5:24 a.m. and set at 8:30 p.m., meaning that there will be 15 hours and 5 minutes of daylight. After that, the days will begin getting shorter as we make our way toward winter.
…but only in the northern hemisphere
In the southern hemisphere, June 20 is the shortest day of the year. Earth has seasons because it’s tilted, so light from the sun changes throughout the year differently for different parts of the world.
The 2024 summer solstice is the earliest since 1796
Usually it’s a decent rule of thumb that seasons start on the 21st of the appropriate month, but that’s not always the case—and this year’s precise moment of solstice is particularly early. The simplest reason why is that 2024 is a leap year. As the Washington Post explains, “During leap years such as 2024, the solstices and equinoxes occur about 18 hours and 11 minutes earlier than the previous year.” During non-leap years, the timing of the solstice moves later, so things generally balance out over time.
No one knows who discovered the solstice
The question of who first figured out that the longest day of the year corresponds to the sun’s highest point in the sky is “spectacularly unanswerable,” Owen Gingerich, Professor Emeritus of Astronomy and History of Science at Harvard University, told TIME in 2016. “No writing to record this great discovery. Lost in the mists of time!”
Read more: Photographing The Longest Day Of The Year Inside Rome’s Pantheon
But ‘Egyptian Stonehenge’ is the earliest indication people knew about summer solstice
About 6,000-6,500 years ago, nomadic cattle-herders in southern Egypt are thought to have arranged stones that line up with the path of the solstice sun in the Nabta Playa basin under the Tropic of Cancer. “[The solstice] was an important touchstone that said, ‘Well, the Nile is about to go into its flooding cycle’ and that would basically start their calendar,” as Sten Odenwald, a NASA astronomer, told TIME in 2016.
The summer solstice is a boon for solar energy
More sunlight in a day means more juice for solar panels, boosting electrical supplies in homes with the setup. On social media, lots of solar power companies will likely be taking advantage of the summer solstice to talk up the benefits of this clean energy solution.
The summer solstice is not the hottest day of the year
This year, the summer solstice corresponds with a record heat wave in many parts of the U.S., so check out TIME’s guide to staying safe. Still, as the New York Times reports, it takes a while for the Earth to heat up each summer, so the hottest temperatures of the year usually take place in July or August.
Read more: See Summer Solstice Celebrations Around the World
People will be playing a lot of golf…
Golf clubs across the country are hosting sunrise to sunset golf tournaments this week. For example, at Bandon Dunes in southern Oregon, golfers usually fit in 72 holes of golf from sunrise to sunset.
…feasting on herring and vodka…
In Sweden, there are all kinds of parties celebrating the summer solstice, in which people dance around a maypole with flowers in their hair, eat a lot of smoked fish, and take shots. “A lot of children are born nine months after Midsummer in Sweden,” Jan-Öjvind Swahn, a Swedish ethnologist, once told CNN.
…And doing yoga
In India, mass yoga sessions take place, drawing hundreds of thousands of participants. As TIME previously reported, it is said that the summer solstice was when Adiyogi, the first yogi, met his disciples. Historically, the United Nations has timed International Yoga Day to the summer solstice.
