—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
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])