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Everything You Need To Know About The Summer Solstice

Here's why the first official day of summer is the longest day of the year for the Northern Hemisphere.

Summer beckons us all year long with the promise of swimming pools, ice cream trucks, and relaxing in the shade. For the Northern Hemisphere, the official summer season starts on June 20 or 21, depending on where you live, with the arrival of the summer solstice.

So what is a solstice, exactly? It's the result of Earth's north-south axis being tilted 23.4 degrees toward the sun. This tilt causes different amounts of sunlight to reach different regions of the planet during Earth's year-long orbit around the sun.

Watch: Sun 101

Take a breathtaking journey to Earth's closest star, the sun.

On the June solstice, the North Pole is tipped more toward the sun than on any other day of the year.

This means that on the June solstice, the Northern Hemisphere will have the longest day and shortest night of the year. (The opposite holds true for the Southern Hemisphere, where June brings the winter solstice and the shortest day of the year.)

Read on for some more intriguing facts about the summer solstice.

MORE SUNLIGHT DOESN'T MEAN MORE HEAT

On the summer solstice, the Northern Hemisphere receives more sunlight than on any other day of the year—but that doesn't mean the first day of summer is also the hottest.

Earth's oceans and atmosphere act like heat sinks, absorbing and reradiating the sun's rays over time.

Even though the planet absorbs a lot of sunlight on the summer solstice, it takes several weeks to release it. As a result, the hottest days usually occur in July or August.

"If you think about turning up an oven, it takes it a long time to heat up," said Robert Howell, an astronomer at the University of Wyoming.

"And after you turn it off, it takes a while for it to cool down. It's the same with the Earth."

THE EARTH ISN'T ANY CLOSER TO THE SUN

Another popular misconception is that during the summer—and especially during the summer solstice—Earth is closer to the sun than at other times of the year, says Mark Hammergren, an astronomer at the Adler Planetarium in Chicago.

In reality, the tilt of Earth has more influence on the seasons than does our planet's distance to the sun.

"During the Northern Hemisphere summer, we're actually farthest from the sun," Hammergren said.

SOLSTICE SPARKED ANCIENT CELEBRATIONS

The summer solstice—also called midsummer—has long been recognized and often celebrated by many cultures. Egyptians built the Great Pyramids so that the sun, when viewed from the Sphinx, sets precisely between two of the pyramids on the summer solstice.

The Incas of South America celebrated the corresponding winter solstice with a ceremony called Inti Raymi, which included food offerings and sacrifices of animals, and maybe even people.

Archaeologists have also discovered the remains of an astronomical observatory in a long-buried Maya city in Guatemala, in which the buildings were designed to align with the sun during the solstices. During such times, the city's populace gathered at the observatory to watch as their king appeared to command the heavens.

And perhaps most famously, Stonehenge in the United Kingdom has been associated with the winter and summer solstices for about 5,000 years.

Observers in the center of the standing stones can still watch the summer solstice sunrise over the Heel Stone, which stands just outside the main ring of Stonehenge. (Read about pagans' campaign to enter Stonehenge on the summer solstice and other sacred days.)

SOME KEEP THE TRADITION ALIVE

But for many modern cultures—and Americans in particular—the solstices and equinoxes are no longer as important.

Most people who "really pay attention to what's going on outside on a regular basis are the neo-pagans in America and farmers, because it's important for their growing and harvest seasons," said Jarita Holbrook, formerly a cultural astronomer at the University of Arizona in Tucson.

Not so for the city of Fairbanks, Alaska, which has been commemorating the summer solstice with a late-night baseball game for 109 years. (See "Pictures: Summer Solstice Marked With Fire, Magic.")

The first Midnight Sun Game, held in 1906, began as a bet between two local bars shortly after a building fire gutted downtown Fairbanks, according to Tom Dennis, the general manager of the Alaska Goldpanners baseball team, which has been hosting the game since 1960.

Every year, a different team—usually from out of state—is invited to participate in the symbolic event.

The game typically begins around 10:30 p.m., continues straight through midnight, and often lasts as late as 2 a.m. Fairbanks, which is located only 160 miles south of the Arctic Circle, gets up to 22.5 hours of summer daylight, Dennis says. North of the Arctic Circle, the sun won’t rise or set, but will stay above the horizon for the whole day.

"We don't need caffeine," he says, "because we have sunlight."