As we celebrate everyone’s favorite Swampscott weekend, July 4th, the days feel endlessly bright. Those dark weeks on the other end of the calendar in late December are safely tucked away, unremembered.
Yet it is that dark time that gives us our current celebration. In one year, every spot on the planet gets 12 hours of light and 12 hours of dark. No one gets any more or any less. The difference lies in how the portions are distributed. On the equator, sunrise and sunset never change.
People living 10,000 years ago knew all about this.
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There is the cave in northern Scotland which traces the trajectory of sunrise, beamed in through a precise hole drilled in the entrance and charted across an inner wall. There are elaborate circles of rock at Chaco Canyon in New Mexico.
But for us, disconnected as we are to the natural cycles of the earth, sometimes we need a little refresher course.
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Which, thanks to artist Bruce Greenwald and the Clifton Beach Improvement Association, is the Sun Circle at Preston Beach.
Those striking basalt pillars that grace Preston Beach Park are literal markers of the sunrise as we pass through the seasons. Look at the four notched pillars placed on opposite sides of the circle.
Standing in the center and looking out, the notch in the pillar on the left indicates where the sun will rise at the summer solstice, which we celebrated last week. This point is the farthest north the sun will rise throughout the year—32 degrees north of east--and brings the longest daylight of the year.
When we reach the solstice the sun rise begins to move back toward the east, rising closer and closer to due east, which it will reach in late the September, the equinox, when the hours of light and dark are equal.
On that day, the sun will rise between the notches of the middle pillars.
The sun continues to rise farther and farther south, until it reaches in late December the winter solstice, 32 degrees south. In the sun circle, the sun will then rise along the notch of the far right notched pillar.
At which point, the sunrise will begin its journey north again, toward the spring equinox and back again to the summer solstice.
The darker pedestal in the middle of the circle delineates the lines of the sun’s rays along this course as well.
Of course, the sun isn’t moving—we on the earth are. We tilt at different angles toward the sun as we rotate around it, spin ourselves, and are circled by our moon.
James F. Keating, astronomer and retired science teacher at Marblehead High School, did the calculations that led to placement of the stone blocks.
At the recent solstice celebration at the circle, he offered up another mindbender. In “a couple of 1000 years” the blocks will be wrong, he said. “The earth wobbles like a top, and every 26,000 years it makes a full cycle, so what to us is the familiar morning star Vega half-way through the cycle will be on the opposite end of the sky,” and the pillars will no longer reflect the actual sunrise.
But we’ll be long gone by then.
For more photos of how the sun passes through notches at the various seasons, visit http://ciabeachbluff.org/suncircle9.html
