How much do you know about summer solstice?

The summer solstice usually happens on June 21, give or take a day or two, every year.

The summer solstice is the beginning of summer, and is the longest day of the year.

In North America, the summer solstice is the beginning of summer.

The phenomenon is called the "midnight sun," when the sun never sets below the horizon for a period of time during the summer months.

The summer solstice, to the ancient Greeks, began the 30-day countdown to the Olympics. Originally just one day, the event was expanded to span five days of events including boxing, equestrian, javelin, long jump, pankration, running and shot put. The circus games, chariot races and "sea battles" were all games played in the Colosseum during the Roman Empire.

Why so much sun in the summertime? That's what happens when the Earth is facing and tilted toward the sun.

The opposite of the Dōngzhì festival is Duanwu, the celebration of "yin" that happens near the summer solstice.

The pair, summer solstice and winter solstice, are also called the June solstice and December solstice, North and Southern solstices, as well as the astrological-derived first point of Cancer and first point of Capricorn.

The ancient Romans celebrated their goddess of the hearth, Vesta, during their Vestalia festival, which lasted over the few days prior to the summer solstice.

Known as the Midnight Sun Game, Fairbanks, Alaska, plays a regulation game of baseball -- with no artificial lights -- that begins at 10:30 p.m. and continues beyond midnight.

Above the equator is the Northern Hemisphere, while below it is the Southern Hemisphere. The seasons are reversed. When it's summer solstice in the Northern Hemisphere it's the opposite -- the winter solstice -- in the Southern.

The Earth's axis of rotation -- the path it takes around the sun -- is tilted at 23.5 degrees. It's this tilt that gives our planet its seasons. When the sun is directly over the Tropic of Cancer, which is located 23.5 degrees north of the equator, it's the summer solstice for Americans. When it's directly over the Tropic of Capricorn, it's the winter solstice.

Dancing around the maypole, a tall pole decorated with greenery and flowers, is a popular summer solstice tradition in countries around the world.

If you were visiting the Arctic Circle (at roughly 66.6 degrees north latitude, around the North Pole) on the day of the summer solstice, you'd see the sun along the horizon, but it never sets.

Litha celebrations are known for their bonfires, either on the eve of or on the day of. For some, it's the fire that brings luck, while others use the ashes for protection and other benefits.

A 20-inch round window above what's called the "altar stone" in the Externsteine is aligned with the sun during sunrise of the summer solstice. But, the purpose of Externsteine, an enormous rock formation near Horn-Bad Meinberg, Germany, remains a mystery.

The sun rises over the eastern horizon, on the day of the summer solstice and every day.

If you stand in the right spot inside Stonehenge, you can watch the sun rise over the stone known as the Heel Stone. On the winter solstice, people gather to watch the sun set below the part of Stonehenge called the Trilithon.

Many countries around the world celebrate the summer solstice, and it has a different name depending on which country you're in. A few common names are Litha, Midsummer Day and St. John's Day -- and all occur on or within a few days of the solstice.

Nope! Earth isn't the only planet in our solar system that has a solstice. Mars, our planet's neighbor, for instance, also has solstices. And the seasons on Jupiter change so slowly, each one lasts about three years.

When you're at the equator all days have the same hours of light and dark. Elsewhere on our planet that only happens on the spring (called "vernal") and fall (called "autumnal") equinoxes.

According to tradition, placing flowers (some say seven, others say nine) under your pillow, if you're unmarried, to dream about your future spouse.

Fire, as bonfires or in fire festivals, is typically used in celebrating on the summer solstice.

On the longest day of the year, the shadow you cast at noon is the shortest shadow you'll have all year.

The summer "solstice" is when, according to its Latin roots, the sun stops in the sky.

Juhannus is the traditional Finnish Midsummer celebration. It's also been celebrated in Kaleva, Michigan, since the turn of the 20th century, when Finnish immigrants settled in the area.

Tucson, Arizona, celebrates the summer solstice with the Earth Walk Solstice festival, which has featured events including a giant labrynth.

Yes, you can balance an egg on a flat surface on the day of the summer solstice -- and the winter solstice, both equinoxes and every other day of the year. It doesn't have anything to do with the Earth's axis. It does have to do with weighing down the bottom of the egg: shaking the egg, place it in the carton to settle, and then stand it up.

It was the ancient Greeks whose new year coincided with the summer solstice. Today we follow the Gregorian calendar.

The Inca celebrated their sun god, Inti, at the Temple of the Sun on the summer and winter solstices. The design of the temple is such that the sun's rays shine through a window at sunrise on the summer solstice.

In European pagan tradition, rubbing fern seeds on your eyelids might help you see faeries on a midsummer's night.

Since 1982 when it began in France, the Fête de la Musique, or Make Music Day, is celebrated on the summer solstice.

Summer, it turns, out, depends on your perspective. To astronomers, yes, the summer solstice marks the beginning of the astronomical summer. But when it comes to summer weather, meteorologists kick summer off as of June 1, based on annual temperature cycles.

Solstice in Times Square is a day-long yoga event on the day of the summer solstice, beginning with sun salutations in the morning and continuing until sunset. It's been going on for more than a decade and was also named the International Day of Yoga by the United Nations.

At the top of Fajada Butte in northwest New Mexico you'll find the Sun Dagger, a set of petroglyphs. On summer solstice, a beam of sunlight hits the center of the main spiral petroglyph.