In his cosmic tragedy King Lear, Shakespeare gives us the Duke of Gloucester, who is convinced that our fates are controlled by the Sun, the Moon, and the gods who “kill us for their sport.” His quote about eclipses would likely have reminded the audience at the Globe in the early 1600s of a series of remarkable solar and lunar eclipses that had swept over England in the previous decade, and coincided with the death of Queen Elizabeth, the ascension of her cousin James (a relative unknown and an outsider from Scotland), and domestic turmoil such as the Gunpowder Plot – today remembered in England on Guy Fawkes Day.

Gloucester’s bastard son Edmund, the charismatic villain and plot driver of what I believe to be Shakespeare’s greatest play, in contrast provides a more modern view of events in the sky, a sentiment that instantly makes me his fan.

This is the excellent foppery of the world, that, when we are sick in fortune, often the surfeit of our own behaviour, we make guilty of our disasters the sun, the moon, and the stars; as if we were villains on necessity; fools by heavenly compulsion; knaves, thieves, and treachers by spherical pre-dominance; drunkards, liars, and adulterers by an enforc’d obedience of planetary influence; and all that we are evil in, by a divine thrusting on. An admirable evasion of whore-master man, to lay his goatish disposition to the charge of a star! My father compounded with my mother under the Dragon’s Tail, and my nativity was under Ursa Major, so that it follows I am rough and lecherous. Fut! I should have been that I am, had the maidenliest star in the firmament twinkled on my bastardising.

Unlike Gloucester, I am looking forward (with some trepidation, more on that below) to a once – maybe twice – in a lifetime event coming on August 21, 2017. Known as the Great American Eclipse, it is the best opportunity so far in my lifetime to experience that rare astronomical event, a total solar eclipse.

On that date, I’ll be driving from my house in Columbus, Ohio at 4 am and heading south, hoping against hope for light traffic and clear skies. I’ll have Carl Sagan and A Midsummer Night’s Dream to keep me company as I head toward the thin line of totality that passes through Western Kentucky and North-Central Tennessee. My current plan is to land just east of Nashville and nestle into a secluded and cloudless spot where I will lose my total eclipse virginity.

Way back in 1994, before marriage and children, I drove on a beautiful day in May to nearby Toledo for another eclipse. That one, however, was an annular eclipse, in which the Moon – slightly too far away at that point in its orbit – didn’t quite cover the entire solar disk, leaving a ring all the way around. It was a moving experience, but left me hungry for the real thing.

The crazy part, of course, is that there’s nothing (from a solar system perspective) particularly significant about an eclipse. In a sense, there’s (almost) always a solar eclipse somewhere, since the Moon always casts a shadow (unless the Moon itself is in the shadow of the Earth, creating a lunar eclipse). It’s just that usually the Moon’s shadow doesn’t hit anything, but merely stretches off into the blackness of space. Had we the Starship Enterprise and the inclination to do so, we could travel about in the Moon’s shadow whenever we wished. For now, though, only when the Earth happens to be in the way of the shadow, only when the Earth’s normal supply of sunlight is suddenly cut off by the Moon, do we here on the surface notice the lunar occultation.

Even so, the descriptions I’ve read from those who’ve experienced it (including particle physicist Frank Close in a book of his I just finished) and the memory of televised totality in 1979 make this an event I have to see for myself, in person. Or at least try.

Two variables beyond my control could, of course, scotch my plan. First of all, initial estimates say that perhaps 100 million people will cram themselves into the path of totality, many of them claiming their spots by Saturday. Others will, like me, begin their quest early Monday morning, jamming the roads into possible impassibility. I may travel hundreds of miles only to be caught on a country road in Southern Kentucky, tantalizingly close but just beyond the totality path. Second, I could get into position only to have clouds or even rain ruin the view. But such is the nature of the quest. You makes your choices and you takes your chances.

You can find all the information you want and then some regarding the science of eclipses on line this week and beyond, so I won’t bore you with too much detail. Just a couple points of wonder, though.

We see our particular brand of eclipses here on Earth due to a remarkable cosmic coincidence. The disk of the Moon just happens to be 400 times smaller than the disk of the Sun. It also just happens to be 400 times closer to us. This results in two disks that, while wildly difference in appearance and properties, are essentially the same size in our sky.

Shakespeare used this cosmic coincidence when Romeo described Juliet as the Sun, the “mate” of the “envious Moon”

But, soft! what light through yonder window breaks?
It is the east, and Juliet is the sun.
Arise, fair sun, and kill the envious moon,
Who is already sick and pale with grief, 850
That thou her maid art far more fair than she:

There’s no particular reason that the Moon, created when a piece of a planet crashed into the early Earth over 4 billion years ago, knocking part of itself and a sizable chunk of the Earth’s mantle into space, and the Sun, containing itself over 99% of the mass of the Solar System, should appear so similar from Earth. In addition, the Moon is slowly spiraling away from the Earth. In another billion years, it will be far enough away that the coincidence will no longer seem so amazing, and the Moon will no longer cover the Sun.

The speed of the Moon’s shadow across the Earth’s surface is amazingly fast, yet not the practically instantaneous speed of a light beam, and this in-between speed has some cool mathematics behind it.

First, the Moon is in motion around the Earth. The speed of that motion is a cool 2300 miles per hour. That’s about twice as fast as an F-18 at top speed. However, the Earth itself is in motion, too. As it happens, the Moon’s revolution and the Earth’s rotation are in the same direction. The result is that the motion of the shadow as perceived on the Earth’s surface is slowed a bit. There’s another effect though – the Earth’s surface is curved. Because of this curvature, in the West the shadow will be much faster than in the East. When the shadow makes landfall in Oregon, it will be moving at 2400 miles per hour – even faster than the Moon in orbit. By the time the shadow reaches South Carolina, it will hit the Atlantic at about 1500 mph.

In his book linked above (Eclipse – Journeys to the Dark Side of the Moon), Frank Close describes watching that shadow as it approaches him just before totality. Not sure if I’ll be able to see this from my eclipse location, but it would be an amazing sight.

For now, though, in my pre-eclipse ignorance, the most amazing thing about the eclipse isn’t the event itself, but our ability to understand it so fully and predict it so completely.

Even in the middle ages, people had become fairly good at predicting eclipses by using rough rules of thumb and noticing patterns. But the work of Galileo, Kepler, and especially Isaac Newton turned eclipse prediction from a rough art to an exact science. Newton noticed the Moon as it moved across the sky and compared it to an apple as it fell to Earth from a tree, and realized that the same force could explain both motions. From there, Newton’s inverse square law

F = GMm/r^2

along with a little calculus, correctly predicted not just eclipses, but the motions of all the planets, moons, comets, and asteroids. Every time we launch a robotic emissary into deep space, it arrives at the exact moment Newton’s Laws says it will. It’s remarkable that so much could come from such a simple-looking formula.

Newton’s Laws were so exact, in fact, that it became big news when anything didn’t obey them precisely. When Albert Einstein was able to modify Newton with his General Theory of Relativity, he experienced palpitations of excitement when his theory, but not Newton’s, matched the precession of Mercury’s orbit. Later, Arthur Eddington observed starlight skimming past the Sun during another solar eclipse (this one in 1919), thereby confirming Einstein’s theory.

In 1974, Joseph Taylor and Russell Hulse observed a pair of neutron stars orbiting one another, losing energy and so drawing closer together (and revolving ever faster) in exact accordance with Einstein’s idea that gravitational radiation carries energy with it in the form of gravitational waves. And today, experiments like LIGO are for the first time actually detecting those gravitational waves, which bathe us always in an almost-indetectable sea of gravitational fluctuation.

These will be some of the thoughts swimming through my own brain as I do my best to rendezvous with that brief shadow of totality on Monday. Wherever you are, enjoy this once (or maybe twice) in a lifetime event. Happy eclipsing!

 

 

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