Don’t want to speak too soon, but summer ends Saturday, and no hurricane yet. The Atlantic is empty of big spinning dervishes, except lonely Nadine, who is not heading our way. She and we might have meant something to one another, but it’s not to be.
Ironically the fall-like air we’ve rubbed all over ourselves recently is about to end also. So the weather forecasters say. The heat’s rising, they say.
We’ve talked about the kind of summer it’s been, but after a brief indulgence we’ve let the subject drop. It’s back to school, get in some firewood, and here’s the autumn equinox. We tend to comfort ourselves by repeating our delight in September and October, the best months of the Vineyard year. But, really, there’s nothing like summer. Summer is what the Vineyard was made for.
The end of summer and equal day and night is scheduled precisely at 10:49 am our time.
These mornings, when we wake at 5:30 am, sunrise is a few minutes away. That will change Saturday when we wake in summer and go to bed in the fall. We have lived through the event and will again, perhaps.
Now, the sun’s early gleam lights the dark windows and limns the waving oaks and evergreens. The trees do as they are told by the wind, unconcerned with the underlying astronomical principles at work in the universe, which includes us. Unconcerned also with the progress of Nadine and our regrets over summer’s end, the sky lights itself in preparation for the big solar moment.
While the coffee makes itself, one of its subjects got out the old, royal blue Britannica — the paper one, not the one on CD. Unlike the thoughtless trees, he wondered what lay in store for him Saturday.
He read: “either of the two moments in the year when the sun is exactly above the equator and day and night are of equal length….” That sounded familiar.
Coffee was ready. He poured it, black, into the large, big-bellied mug with the reclining English mastiff on the side, and he read some more.
“Also, either of the two points in the sky where the ecliptic (the sun’s annual pathway) and the celestial equator intersect…. The autumnal equinox falls about Sept. 23, as the sun crosses the celestial equator going south.”
Oh, he thought, that equator, not the one on all the globes.
The coffee was stronger than he had planned, and there were still a few moments before the sun flies by. He added milk. The dogs were sitting expectantly. What did they want? A walk, or some food.
Before he could decide, his eye fell on this: “Some astronomical coordinates…are measured from the vernal equinox. It is sometimes called the first point of Aries because it was at the beginning of that constellation some 2,000 years ago. The term is still used, though precession of the equinoxes has moved the vernal equinox into Pisces.”
If these equinoxes are preceding, he thought, how does anyone know that the moment will be at precisely 10:49 am on that fateful day? Are there no seconds involved here? How could there not be?
That’s when he came upon the business about wobble. We’re wobbling, the equinoxes are preceding, there is really a great deal going on. These dogs will just have to wait.
Although we haven’t thought much about it, everybody has known about it since before 129 BC, when the Greek astronomer Hipparchus “noticed that the positions of the stars were shifted in a systematic way from earlier Babylonian (Chaldean) measures.” But it wasn’t the celestial arrangement that was moving, it was earth, our observatory and vantage point.
Precession, the third-discovered motion of the earth, along with daily rotation and annual revolution, “consists of a cyclic wobbling in the orientation of the earth’s axis of rotation with a period of almost 26,000 years.”
The gravitational influences of the sun and the moon do it to us, and because of this wobbling the celestial poles of the earth trace out circles on the sky, and the “equinoxes drift westward along the ecliptic at the rate of 50.2 arc seconds annually as the celestial equator moves with the earth’s precession.”
Wobbling and drifting (in a fashion not unlike his own early morning progressions) the earth and the sun have conspired over this equinoctial instant. We count on it, distant and unknowable as it is. It means something to us, although while we may have recorded its measurement we have not approached the why of it.
He recalled an arrival at Bermuda years ago after a stormy, mostly cloudy sailing trip. The sun had been elusive.
It was night as the yacht approached the narrow entrance channel and its tumbling sea buoy. The navigator, without global positioning system, radar, or radio direction finder, mostly without star sights, and even days without sun sights, had somehow found this speck on the wobbling, watery globe. For which he remembered being terribly grateful. And as he recalled the gladdening events of that dark, heaving evening, he briefly lost track of the time.
And now we learn, according to C. Claiborne Ray, writing Tuesday in the New York Times, that even more of what we thought was fixed, true, and dependable is varying, uncertain, and qualified. The melting of the polar ice is distorting the very earth.
“This net mass shift [of frozen to liquid water] slows the Earth’s spin rate, just as a spinning ice skater pushes out her arms to slow down.” [This according to James Davis, Lamont Research Professor at the Lamont-Doherty Earth Observatory of Columbia University.] “That has the effect of lengthening the day: Recent calculations indicate that loss of mass in Greenland and the Antarctic makes the day about 0.6 milliseconds longer per century.”
And as if this were not unsettling enough, Mr. Ray goes on, “At the same time, however, Earth is still changing shape in response to the massive melting from 23,000 to 10,000 years ago — coincidentally decreasing the day by about the same 0.6 milliseconds per century.”
Is there nothing we can count on? Each sunrise and sunset, we had thought, was a triumph of celestial precision over wavering and uncomprehending mortal vigilance. And, now this.
Only the dogs, fixed stars in his firmament, had maintained their appealing focus, insisting, as such creatures always do, on just exactly what matters most.