The newly opened Sweetwater Park on Chula Vista’s bayfront has a very unique architectural feature.
At one end of the public restrooms a sheltering roof contains an oculus. What’s an oculus? It’s a circular opening that allows natural sunlight to shine through.
During the day, the oculus casts a circle of light on bands in the concrete underfoot. You can see those curving bands in the above photograph.
By observing the light’s movement along the bands, Earth’s rotation can be tracked, as the sun “rises” in the east and “sets” in the west. Depending on the season of year, and the angle of the sun’s path through the sky, the projected light will follow a particular band.
On the wall is an explanation…
The Theory of the Seasons.
The Earth’s rotation axis is tilted by 23.5 degrees with respect to the ecliptic and is always pointed to the celestial poles as the Earth moves around the Sun. Sometimes the Northern Hemisphere is tilted away from the Sun and the Sun’s rays hit the Northern Hemisphere at a shallow angle.
The Summer Solstice marks the beginning of Summer and is the longest day of the year, just as the Winter Solstice marks the beginning of Winter and is the shortest day of the year.
The Equinoxes; Equi meaning Equal, and Nox meaning Night, telling you that the day and the night are of equal length. This occurs when the Sun is directly over the Equator, in between the two Tropics and occurs around March 21st and September 23rd marking the beginning of Spring and Autumn.
If this sounds like a whole bunch of mumbo-jumbo, fortunately there’s an illustration to help one visualize the concept…
Now consider my next photograph.
On June 21, as the summer begins, the sun will be at its highest in San Diego, here in the Northern Hemisphere.
Because of this, the sun’s light projected through the oculus will come from a high angle, and follow the lower band as Earth turns and the day progresses.
It just so happened that I visited Sweetwater Park on June 18. I arrived at the oculus a little after noon.
You can see the circle of light is almost atop the June 21 band, and is now to the right of the central drain, past the 12 PM mark.
The light would continue to move right along the same band as the sun descends in the sky toward the horizon.
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