When the Earth Tilts

September 23, 2018February 12, 2019

The sun sinking slowly due west with the moon rising in the east made it seem as if the earth were tilting. I reached out with one foot to steady myself as on a leaning ship. The rotation of the earth never seems more graphic than on those magical evenings.

I’ve experienced this vertiginous illusion before at the park, but not on a special night like the Autumnal Equinox, Saturday evening Sept. 22nd. What’s more, the moon stood just a faint sliver short of fullness; a Harvest Moon will rise Sunday night. It’s rare for a Harvest Moon to happen so near to the Equinox. Even more unusual, a quartet of planets — was it Mars, Jupiter, Saturn, and Venus? — stood ready to appear in an arc across the night sky, and would have done so but for a herd of cloud sheep that wandered across the view, as sheep will. All this astronomical fireworks came, as if by cosmic intent, on the twentieth anniversary of astronomical observations at the Chavez Solar Calendar.

The expected appearance of members of a Fremont Hindu congregation for a demonstration of the Chhath Puja festival fell through at the last hour, but Rabbi David Cooper, a veteran of Solar Calendar celebrations, almost made up for it with an illustrated and choreographed field lecture on the Equinox, including the points mentioned in my opening paragraph. Cooper held a globe in its tilted position (about 23.5 degrees) and walked it around the calendar’s gnomon, and then around a volunteer Sun-person, to show the distribution of light and dark over the course of one revolution around the sun. That’s how we get seasons, and how the seasons up north are the reverse of those below the equator.

Cooper is a deep fount of astronomical and historical knowledge. Before the magic moment when the sun exactly passed the equator and our season shifted from summer to fall, Cooper also showed how the positions of sunrise and sunset on the local horizon moved from the winter solstice to the summer solstice, how the solar calendar shows the exact date at solar noon, how Galileo demonstrated the truth of the Copernican thesis that the earth revolves around the sun, and much else. And then, at the decisive instant, Cooper raised a twisted ram’s horn to his lips and blew a salute to the death of summer and the birth of autumn. Among the appreciative audience stood Solar Calendar founder and curator Santiago Casal.

It just doesn’t get much better than that.

When the Earth Tilts

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