Summer Solstice Facts: Why It's Early This Year, More

Brian Handwerk
for National Geographic News
June 19, 2008
On Friday, June 20, the summer of 2008 will begin in earnest across the Northern Hemisphere with the longest day of the year. This year is unique in that the solstice has not occurred before June 21 since 1896. The early arrival—albeit only by a minute—is due to a complex quirk of the leap-year calendar.

Before the sun sets on the June solstice, get the facts on why it occurs and how people throughout history have celebrated the event.

Celestial Science

—The word solstice's Latin roots mean "sun stands still," an apt description of how the astronomical event appears from Earth.

Since ancient times people have followed the movement of the sun as it rises, crosses the sky, and sets along a path that changes incrementally throughout the year.

For a few days surrounding the solstice, however, our star seems to rise and set at the same locations. It also hovers at the same noontime spot, pausing before its trajectory begins its incremental shift until year's end—the December solstice.

—The "summer solstice" should be called the "June solstice," because it is actually the winter solstice in the Southern Hemisphere. Despite the reversed seasons, the event has long been observed south of the Equator as well.

—Winter and summer occur largely because the planet is tilted on an axis running through the poles at an angle of 23.5 degrees. As the planet orbits the sun, each hemisphere receives varying amounts of light and warmth determined by the direction in which it is tilted: summer when tilted towards the sun and winter when tilted away.

(Read more about Earth's orbit.)

On June 20, 2008, the North Pole will tilt most directly toward the sun, so that the noon sun appears at its highest point in the sky—nearly directly overhead. This is the year's longest day in terms of daylight hours.

(Related story: "In Scandinavia, Solstice Means Fun in the Midnight Sun" [June 21, 2005])

At the same time, in the Southern Hemisphere, the pole is tilted farthest away from the sun, and the June solstice falls in winter, marking the shortest and darkest day of the year.

—The Northern Hemisphere soaks up more sun on the June solstice than on any other day, but the period surrounding the solstice is not as hot as the later months of July and August when daylight hours are actually waning.

That's because at solstice time the hemisphere is still warming up after a long winter—just like a summer day is still warming at noon and will be hotter in midafternoon.

In June some ice and snowmelt continues, and ocean waters are still warming, as the hemisphere moves toward the truly hot days later in the summer.

—The sun's movements are especially pronounced in the polar regions.

North of the Arctic Circle the solstice heralds the arrival of 24-hour sunlight. The effect lasts longer the further north one goes—culminating at the pole itself.

At the North Pole the sun rises on the spring equinox—around March 21—and does not set until the fall equinox on or near September 21. As elsewhere, it climbs to its peak at the June solstice.

—The solstice occurs at the same moment all over the planet. But because earth is divided into some two dozen time zones, people experience it at different times of day.

This year's event occurs on June 20 at 11:59 p.m. (23:59) Universal Time Coordinated (Greenwich, England).

How the Ancients Marked the Day

—The solstice is commemorated in stone on Egypt's Giza plateau. The summer solstice sunset, as viewed from the Sphinx, sets precisely between the two Great Pyramids.

Egyptian adepts were attuned to the solstice because it often coincided with the annual Nile River floods that were so critical to agriculture in the river valley.

They learned to predict this annual event by tracking astronomical signs, including the rising of the bright star Sirius.

(See a photograph of a well near Aswān, Egypt.)

—North American Indians celebrated the solstice at sites such as Toltec Mounds Archaeological State Park near Little Rock, Arkansas. There the solstice sun sets directly behind a ceremonial mound constructed some thousand years ago.

—The Nazca Lines, a mysterious series of shallow trench designs dug in the Peruvian desert between 500 B.C. and A.D. 500, include features aligned with both the summer and winter solstice sunsets. This discovery gave rise to the disputed theory that the massive designs, which include the figures of animals, plants, and other beings visible only from the air, were dedicated to astronomical observation.

—The solstice was particularly meaningful for the Inca, who believed that they were descended from the sun god Inti. Their two major religious ceremonies were held during the solstices.

The June solstice was celebrated with a ceremony called Inti Raymi (see photo) in which offerings of food, animals, and perhaps even people were made.

Since the 1940s the holiday has again become a major celebration in Cuzco and is popular with vacationers—though the sacrifices are not what they used to be.

The famed ruins at Machu Picchu also include a semi-circular structure called the "Temple of the Sun" that was constructed around a large boulder. During the June Solstice, the sun shines through a temple window and aligns with both the boulder within and the tip of a nearby mountain peak.

(Related story: "Machu Picchu's Mysteries Continue to Lure Explorers")

The arrangement may have formed an ancient sighting device. It also links the sun, mountains and ancient rock as important aspects of Inca religion.

—Stonehenge has been aligned with the solstice for some 5,000 years. Observers in the center of the famed circle can watch the June solstice sun rise over the Heel Stone, which stands vertical just outside the monument.

Thousands of New Agers, Druids, Wiccans, sun-worshipers, and party people still congregate at the monument each year to mark the solstice.

(Related Photo: Stonehenge Revelers at the Winter Solstice [December 28, 2006])

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