On Wednesday, we reach the summer solstice. The first day of summer. The longest day of the year.
It's scientific: The solstice is an astronomical event, a day of solar significance. It's also spiritual: Around the world and throughout history, rituals and celebrations have been tied to the solstice.
For solstice specifics, we talked to Carolyn Sumners, vice president of astronomy and the physical sciences at the Houston Museum of Natural Science, and Eric Schlegel, professor of physics and astronomy at the University of Texas at San Antonio. We also checked with Emilee Dawn Whitehurst, executive director of Rothko Chapel, which will celebrate the summer solstice for the first time this year.
As we prepare for a long, light-filled day, here's a look at what the summer solstice is all about.
The summer solstice is the longest day of the year because it has the longest period of sunlight: Here, the sun rises at 6:21 a.m. and doesn't set until 8:25 p.m., giving us more than 14 hours of light.
What causes the solstice?
The Earth is always tilted on its axis at 23 1/2 degrees, Sumners said. It orbits around the sun in that position -- and in the Northern Hemisphere, when that tilt leans toward the sun, we call it summer. "We are reaching that point in the Earth's orbit where we are tilted most toward the sun," Schlegel said. And when we get there, that's the summer solstice.
So will the sun be directly overhead Wednesday?
Nope -- not in Houston. At the Tropic of Cancer, a line around the Earth that hits just north of Cuba, the sun will be directly overhead. For a brief time there -- and only there -- on Wednesday, nothing will cast a shadow.
We're too far north to witness that phenomenon. We'll come closest, though, at "solar noon," when the sun is highest in the sky. That'll happen at 1:21 p.m.
Doesn't the sun know that noon is at 12 p.m.?
It's an hour later because of Daylight Saving Time, which is in effect this time of year. And on top of that, Houston is about 21 minutes west of the time-zone meridian. In other words, the sun gets to us 21 minutes later than it does to the folks on the eastern edge of the Central Standard Time zone. We're always just a few minutes behind the time our watches display.
What does the sun's position mean for us?
It means a lot of intensity. "The higher the sun is in the sky, the more solar radiation we get," Sumners said. "You'll get your quickest sunburn on the summer solstice -- the sun is most intense." In other words, wear some extra sunscreen.
Isn't the solstice usually June 21?
Yes, but it's June 20 this year. That's a calendar thing, Schlegel said. The Earth takes 365 1/4 days to orbit the sun. That's why we have leap year every four years, including this one. And that means there are adjustments to the calendar that will occasionally throw the solstice off a day.
Why is the solstice a spiritual time?
"Certainly, the longest day of the year has been recognized around the world in spiritual and religious traditions," Whitehurst said. "That's part of why the Rothko Chapel is joining the celebration this year."
For many cultures, the solstice was a celebration of agriculture -- acknowledgment of the sun's role in growing crops. It also marked the passing of the sun, which had reached its peak for the year. Even today, to mark the solstice is to acknowledge that the days will get shorter now and winter is on the way.
For the ancient Egyptians, the solstice generally marked the start of the Nile's flooding season, when the river overflowed its banks and enriched the soil. The Incas celebrated Inti Raymi, the multiday Festival of the Sun, to mark the solstice. The ancient Greeks, too, celebrated with festivals -- and they scheduled the Olympic games to begin after the event had come.
Do people still celebrate the solstice?
Absolutely. In the United States, summer solstice parades and festivals are scattered across the country, including Seattle, Santa Barbara, Calif., and Long Island City, N.Y.
England is home to the most famous celebration: Each June, thousands gather at Stonehenge the night before the summer solstice. They wait all night for the sun to come up over the stone monument; it lines up perfectly with the outer Heel Stone.
There's dancing. There are bonfires. Why such a celebration at Stonehenge? In that part of the world, the seasons are sharply different, Sumners said.
"The more north you are, the more you care about the sun being high in the sky," she said. "When the sun is highest in the sky in Britain, the difference is dramatic."
Even in Texas we'll find ways to worship the sun Wednesday. And we see plenty of it down here.
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