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About Astronomy And Learning To See

for the JSC Astronomical Society at the Lunar and Planetary Institute, 
7:30 PM, Friday, August 28, 1998

by John H. Lienhard
Mechanical Engineering Department
University of Houston
Houston, TX 77204-4792
jhl [at] (jhl[at]uh[dot]edu)

Photo of the Ring Nebula, courtesy of the JSC Astronomical SocietyYou in the JSC Astronomical Society reflect an almost atavistic quality of the human race. The need to look upward at the stars is primordial. I didn't really understand that until my wife and I visited Brazil. Our first evening there was a barbecue at our host's house. 

As we sat outdoors the the stars came out, and suddenly a terrible disorientation came over me. I looked up at that southern-hemisphere sky, and it was wrong. I'd taken fairly little notice of my own northern night sky. But, it seems, it was far more deeply ingrained in my unconscious mind than I'd ever dreamed. 

So tonight I'll argue that astronomy is about changing what we see, not just when we look at the heavens, but when we look around us here on earth as well. I'll begin with a fascinating take on what happened to me that evening in Brazil. Some years ago, science historian Jacob Bronowski posed the question, "Why did astronomy develop in the old world, but not in the new one?"

No southern hemisphere people developed astronomy. The only people in the Americas to do astronomy before Columbus were the Aztecs, and their astronomy was only about calendar-keeping. The Aztecs didn't invent planetary models. They didn't use stars to navigate.

Mediterranean civilizations knew the world was round centuries before the birth of Christ. But that idea never occurred to people in the New World or in the southern hemisphere. Bronowski asks, Why not?

He suggests that two elements drove the development of astronomy. One was that great celestial flagpole, the North Star. It was the point of reference to people in the North. The starry host I saw that evening in Brazil was, by comparison, random and uninteresting.

The Aztecs had the polestar to guide their thinking. They had mathematics. And they took an interest in the heavens. Yet they didn't develop theories and models for astral movement. So Brownowski points out a second missing element outside of Europe, Asia, and North Africa. It was the wheel, that strange device, so simple to those who know it and so unimaginable to those who don't. The wheel led us to see the rotary motion of planets and of a round earth. The steady rotary repetition of planetary and astral positions gave ancient sailors courage to step away from shore and modern astronauts courage to step away from air and away from gravity.

Bronowski finally takes us to Easter Island. That primitive, landlocked, land-imprisoned people came from north of the equator 1200 years ago, and then they lost their ability to sail and to navigate. There they gazed at a featureless sky. They reduced themselves to making huge statues of identical faces — forty-ton monoliths called Ahu, with their backs to the sea, gazing inward on a world complete in itself — a world which, unlike ours, did not open up to infinity.

Of course the story of Easter Island was more complex than that. Still, with its sad stone faces, it becomes Bronowski's metaphor for a world without the wheel and without the polestar. Without these two triggers to the imagination, more than just astronomy is missing. The whole dream-driven technology that shapes our world is absent. With no polestar or wheel, Easter Island life itself grew featureless.

I'd like to digress for a moment to look at the wheel and its relation to all this. The wheel was invented around 5500 years ago. But what was that invention, really? Think for a moment about the concept of rotary motion. The human wrist/arm configuration allows 360-degree rotation. That's why hand drills, using back and forth hand motions, are among the oldest tools.

Late-stone-age artisans extended that rotation with various pivoted devices. A primitive spinning spindle pays out wool or flax fibers from a distaff, while the operator keeps it moving with thumb and forefinger. Early doors, with a vertical shaft on one side, were anchored in sockets that let them swing open and shut.

The next jump in sophistication was using bowstrings to drive back-and-forth rotary motion of drills and fire starters. Those devices all ran one way to a limit. Then they had to unwind. Continuous rotation was the conceptual hurdle. That's why two such devices, the vehicle wheel and the potter's wheel, arose about the same time.

A potter's wheel is a horizontal turntable that holds a lump of clay and turns at at least 100 rpm. The oldest one we know about turned up in the region of the Tigris and Euphrates Rivers (present day Iraq) around 3300 BC.

The earliest vehicle wheel turns up in a cuneiform document from the same region in 3500 BC. Those dates are close. So (to the best of our knowledge) not just the wheel, but continuous rotation itself, dates from five-and-a-half millennia ago in the Fertile Crescent of the ancient world. Another invention, closely akin to the wheel, was the compass for making circles. The first hinged compasses also trace to that same region, 5500 years ago.

Early wheels show a progression of understanding. The first wheels were cut from large wooden slabs, built up of boards. In other words, the lay of the wood seems to fight the rotary motion it's meant to accomplish. Not until 2000 BC do we find wheels with spokes. The spoke itself introduces a new subtlety since it's loaded in tension, not compression. A vehicle hangs on the wheel's upper spokes; it doesn't ride on the lower ones.

Other questions of rotation had to be answered: Wheels are best left free to rotate on a fixed axis. If they're anchored to a rotating axle, then they can't turn at different speeds going around a corner. The idea of a swiveled front axle, one that can turn in the direction of a curve, is barely 2000 years old.

The author first studies the wheelSo it's not the wheel itself but the problem of rotation that dogged our minds for thousands of years. What the ancient Sumerians did was to recognize the problem. And we have (if I may) spun out the subtle ramifications ever since. 

The point is that Earth's roundness was a concept that followed easily for people who'd already taken rotation to anything as sophisticated as the wheel. That roundness and all its implications were an impossible hurdle for any people who didn't have the concept. 

I suppose that gets us to the Columbus question. What did Columbus know, what did he surmise, and what about the people around him?

Columbus sailed off with one part courage and two parts madness to sail around a spherical world. Every educated person knew the world was round, of course. This flat world stuff is pure baloney. Someone cooked up the myth that we all thought Earth was flat during the 19th century.

Still, Columbus's trip was based on a terrible miscalculation. He underestimated earth's diameter, and he overestimated the width of Asia. He thought Japan lay only 2700 miles west of the Canary Islands. A correct calculation would've put it 10,000 miles away, far beyond the reach of any 15th-century ship. Columbus had access to a far better estimate of earth's size, but he failed to use it. Let's look at that for a moment:

A formal understanding of the round Earth came in stages. Twenty-six hundred years ago, the Pythagoreans argued by induction: The moon is round. So is the sun. Surely Earth must be round, as well. Two centuries later, Aristotle argued from observation. When a boat sails off in any direction, its hull always disappears before its sails do. The hull is obviously being obscured by curvature, so the earth must be round.

Science writer John Noble Wilford notes that going from flat to round meant carving earth down from indefinitely large to a much more confined place. The longest journey on a round earth will sooner or later take you back where you began. The round earth had somehow been made into something less than the flat earth was, but how much less?

The Egyptian Eratosthenes, director of the Library in Alexandria, finally wedded observation to calculation around 200 BC. His idea was as simple as it was brilliant: When the sun was directly above Aswan, 500 miles away, he measured the shadow cast by a vertical tower in Alexandria. The rest was simple trigonometry. He calculated earth's diameter with only sixteen percent error, and his method was used right down to modern times.

So mystery had been removed. Earth was now within our grasp. If we could understand Earth, perhaps we could ultimately control it as well. Of course, Columbus wanted the earth to be smaller, so he deceived himself. He was no scientist. In a sense, he wanted to conquer the earth, so he carved it down to fit himself. The crowning irony was that two new continents intervened, and he succeeded.

Yet as Earth shrank, the heavens opened up. Try this question: Why did Copernicus and Galileo follow so soon on Columbus's heels? I think there's a huge gulf between knowing Earth is round and having experienced that roundness. Once Columbus provided that experience, the stage was set for a new science of astronomy.

The story of heliocentricity has been told too many times. So I'll simply tip my hat to that part of the story and pass on to a matter I find more interesting — the matter of seeing the makeup of the planets in a new light.

When Galileo was 25 years old, he applied for a job teaching mathematics at the Florentine Academy of Design. He didn't get the job, but the very fact that he went after a post in Florence's major art academy is important. Galileo was a serious artist and a master of perspective technique. Twenty years later he found an important use for that ability.

His artist's eye finally cut through our inability to see the moon's surface for what it was. Aristotle's moon was a perfect sphere, and that's how people still saw it in 1609. A perfect sphere, of course, is perfectly smooth. The pure moon was not of base earth. The 16th-century Church had used it as a symbol for the Immaculate Conception. In 1609 an innocent was not called pure as the driven snow, but rather pure as the moon. People thought the markings they saw on its surface were merely mirror images of the imperfect earth.

Then an Englishman, Thomas Harriot, got his hands on one of the new Dutch telescopes and produced a crude sketch of the moon's surface. He drew the terminator, separating light and dark, as a jagged line. But Harriot didn't suggest that the moon's surface itself was jagged. Instead, he was puzzled as to why a jagged line would appear on a smooth sphere.

Five months later, Galileo turned his own homemade telescope on the moon. He hadn't yet seen Harriot's sketch, and he had two advantages. For one thing, it was he who'd already put in motion a revolution that would overturn 2000 years of Aristotelian thinking. He wasn't committed to a perfect moon.

Galileo's drawings of the moonGalileo's second advantage was his art. He made a set of sepia drawings of the moon in its changing phases. They were beautiful drawings with a wondrous luminescent glow. Yet they left no doubt about the pockmarked surface. When others saw his drawings, they promptly saw what they hadn't been able to see before. Their moon changed from smooth to rough in a blink. like the shift in an optical illusion. 

Galileo went on to calculate the height of lunar mountains from the shadows they cast. In no time, contemporary poets like Milton, Donne, and Dryden were writing about the craggy lunar surface. By 1612, when the Virgin appeared in a painting on the ceiling of a new Roman basilica, she was now shown standing on a cratered moon. 

Galileo passed this brush with the Church safely. His troubles with the Vatican still lay ahead. His attacks on Aristotelian thinking would eventually lead him into serious trouble. But he won this part of the battle unopposed. 

In 1605, four years before Galileo changed the moon, the famous Jesuit missionary to China, Matteo Ricci, wrote the Vatican asking them to send a mathematical astronomer to join him in Peking. He'd found the Chinese very interested in the subject. They'd already soaked up everything he had to offer. He got his astronomer eight years later. By then, Galileo had become famous for his telescope work. The man Rome sent to Peking was Galileo's student. (Galileo's stock had risen very high in the Catholic Church.)

Some scholars sensed that his work was leading up to the destruction of Ptolemaic astronomy (which was part of Catholic theology). But the issue of a sun-centered solar system hadn't arisen yet. For the moment Rome was fascinated.

After Galileo discovered the imperfection of the moon — after he'd shown that it wasn't sublime empyrean matter after all — he next found that the sun had spots. Western literature often credits Galileo with discovering sunspots. In fact he wasn't by any means first to see them. Islamic scientists had seen them. So had earlier Europeans. But the sightings in the West had been made and forgotten, since they didn't fit the general conviction that the heavens were perfect.

The Chinese had no such illusions about the heavens. They had no problem with imperfect planets. Sunspot observations in China were continuous right back to the 4th century BC. Historian Joseph Needham finds 112 references to sunspots between 28 BC and the death of Galileo, and that's in official histories alone. None of that needed help from Galileo's telescope. The Chinese were quite ready to see what they saw.

By the time Galileo had fallen from grace and gone on trial in Rome, his telescope and his ideas had found their way to Japan. The Japanese put a telescope in Nagasaki harbor to warn against approaching foreigners. They hadn't much cared about the heliocentric universe before all the fuss, but now they claimed Japanese scholars had discovered it. They even claimed that the idea was part of their own ancient religious orthodoxy.

So the great revolution of astronomy began. Galileo's sight was permanently damaged by looking at sunspots through his telescope. Controversy flared among the Jesuits. Revisionist history sprang up in Japan. And the practical Chinese took up telescopy to direct field artillery.

Now let's trace another great scientific shift in perception which flowed from this new astronomy of scientific observation. This one has to do with the speed of light. The speed of light is something we've figured out only in the last century, right? Before the likes of Einstein, we surely knew nothing. Well, once more our forbears surprise us. It turns out we've known the speed of light since before the birth of Johann Sebastian Bach.

That knowledge came close on the heels of Galileo. In 1644, Ole Roemer was born in Jutland, Denmark. He took up the new study of astronomy with the early greats of that field. By 1675 Roemer was 31 and working in Paris. He was interested in the movement of Jupiter's nearest moon. He tracked it as it orbited in and out of Jupiter's shadow. It entered the shadow, then 42 hours, 28 minutes, and 35 seconds later it re-emerged.

It moved with metronomic regularity — with all the clockwork perfection we were now seeing in God's firmament. In one hundred transits, Jupiter's moon would be relied on to emerge once more, right on schedule. In six months, 100 laps later, Roemer set his clock and focused his telescope on Jupiter. He waited. No moon! Minutes passed. No moon. Finally it danced out of the shadows a full fifteen minutes late.

So Roemer considered what might've happened. Earth had swung hundreds of millions of miles away from Jupiter during the long winter months. Light had to travel that vast distance. It'd obviously taken the extra time to do so. He put pencil to paper and found light had to move 192,500 miles per second to lose just fifteen minutes. Not bad! Roemer was accurate within three percent. And that was less than seventy years after we first had telescopes. Just to be sure, he calculated when we'd get that fifteen minutes back as we swung back toward Jupiter. He was right again.

I came on all this reading John Tyndall's 120-year-old text Light and Electricity. Tyndall tells Roemer's story. Then he quotes more recent estimates of the speed of light. By then, one of those more modern estimates was worse than Roemer's. And so your great-grandparents really had no better knowledge of the speed of light than we had when Isaac Newton was still young. Astronomers had first rendered the planets into the same stuff as base earth. Now they'd shown that light was subject to limitations as well.

It's sobering to reflect on the knowledge of our forbears. We knew the diameter of earth within 16 percent, 2000 years ago. We've done brain surgery and cataract operations even longer than that. And so, it seems, there was life before the computer — before Einstein, before the Industrial Revolution. I'm constantly awed by how much we knew so long ago.

The 17th century was the age when all this astronomy began coming together. By the end of the century, astronomy was a household industry. In Roemer's time, one Northern European astronomer in six was a woman — often the widow of a householder who'd taught her the art. Women have been deeply involved in astronomy ever since, although much of that involvement had to begin on the fringes. Let's look at that for a moment.

In 1670, five years after Roemer began the demystification of light by giving it a finite speed, King Charles II took a mistress. She was neither his first nor his last, for that was a way of life among the ruling classes then. (Nothing like that goes on anymore today, of course!) She was Louise de Keroualle, a dark-haired beauty from Brittany in France. She bore him a son two years later, and he made her the Duchess of Portsmouth. The Duchess was the King's clear favorite. But some people feared he might be letting a French spy into the English court.

By now, a new scientific question was gathering importance. This was the age of navigation. European ships were ranging the oceans. It was easy enough for navigators to fix their latitude. But no one knew how to fix longitude. That was the uncertainty that should've killed Columbus, 180 years earlier, and it continued to cause untold trouble among seafarers.

The King had recently created the Royal Society to advance science. Now the Society urged him to build an observatory. We needed better astronomical data to solve the longitude problem. The proposal was foundering in red tape. Then the Duchess produced a friend from Brittany. He was an amateur astronomer named St Pierre.

Once in the English Court, he claimed he could calculate longitudes. In December, 1674, the King set up a Royal Commission to study St Pierre's method. It included such heavy hitters as Christopher Wren and Robert Hooke. But for astronomical advice, they turned to a young man, only 27, named John Flamsteed.

Flamsteed saw that St Pierre's method was inherently inaccurate. Worse yet, he'd taken it from two other astronomers, long dead. When Flamsteed questioned St Pierre, he found that the fellow didn't even understand the method he was proposing. Flamsteed reported to the King that England would have to get longitudes by another method entirely. And that would take far better data on locations of stars and planets than were available. Flamsteed's answer to St Pierre made it crystal clear that England urgently needed a proper observatory. King Charles reacted. That very day he signed the warrant to build the Greenwich Observatory. England was about to set up the world benchmarks for longitude and time. So the Duchess's friend St Pierre went back to France. We don't hear from him again. Yet he and the King's mistress had precipitated one of the important scientific projects of all time. Ten years later, the King elevated another mistress to the aristocracy. He named her, and not the Duchess, the Countess of Greenwich. Thus the King and his court swirled about and played their roles. In the midst of it all was quiet John Flamsteed, one of the great astronomers of all time. The longitude problem would soon revolve around a competition between astronomers and clockmakers, and Flamsteed would be a key mediator in the early days of that debate.

But the other issue was women's struggle to find a legitimate place in the field. So I'll finish with the story of America's first Royal Prize in astronomy. Nobel prizes weren't given until 1901. Throughout the 1800s royal medals were the medium of scientific recognition.

Americans were latecomers to big-time science. Yet we had our first royal prize in astronomy by 1850. It was the Danish Royal Medal, and the winner was Maria Mitchell, who won it for discovering a new comet in 1847. She was only 28 when she did the work.

Photo of Maria Mitchel, courtesy of Helen WrightMitchell was raised by a Nantucket Quaker family. Her father worked at many jobs by day; but he was an astronomer by night. It made a curiously right combination for young Maria. Nineteenth-century Quakers took the education of girls seriously. The seafarers of Nantucket took astronomy seriously. And Maria Mitchell's father took her seriously. She started helping with his observations when she was 12. Maria was working in a library by day and star-gazing by night when the Medal opened doors for her. She became the first female member of the American Academy of Arts and Sciences.

The Nautical Almanac Office hired her to do calculations. She went about as far as any woman could go, 140 years ago. Then Matthew Vassar set up a college to provide women with an education as good as men's. He hired Maria Mitchell, now 47, as the first astronomy professor at the new Vassar College.

Up to then she'd been shy and quiet. Now she had to stand up and talk to people. She took to the new role. And astronomy turned from an end to a means. It was the means by which she could stir up her students' minds. And stir them she did. All the while her interests expanded to larger questions about women in science. She helped form the Association of Women. She was the second president.

We've all but forgotten Maria Mitchell today. She didn't make it into our textbooks. But pioneers seldom get into textbooks. Pioneers help others get there while they remain invisible. For example, a woman named Annie Jump Cannon set out with one of Mitchell's students to classify stars by spectral means. That led to a great ordering of the heavens. Annie Jump Cannon does appear in encyclopedias and texts. She, and others like her, followed Mitchell, and they gave substance to her dreams.

Astronomy is an odd field. Down through history, women have been a major but often invisible part of it. One of the many photos of Mitchell shows her near her 60th birthday. She sits under the lens of the Vassar telescope. She looks like Whistler's mother, stiff and formal under the lens of the camera. But her face is composed.

It is the face of a woman who knows full well that, once more, she too has done what astronomers down through the ages have done. She's altered all we see — in the heavens and to the left and right of us — by gazing through the lens of a telescope.

The new Philosophy calls all in doubt
The element of fire is quite put out;
The sun is lost, and the earth, and no man's wit
Can well direct him where to look for it.
                                 John Donne


Bronowski, J., The Ascent of Man. Boston: Little, Brown and Company. 1973, Chapter 3, The Starry Messenger. This is also available on videotape and film.

Childe, V. G., Rotary Motion. A History of Technology, Vol 1, From Early Times to Fall of Ancient Empires, (S. Singer, E. J. Holmyard, and A. R. Hall, eds). New York: Oxford University Press, 1954, Chapter 9.

Williams, T. I., The History of Invention., New York: Facts On File Publications, 1987, Chapter 4.

Wilford, J. N., The Mapmakers. New York: Random House, Vintage Books, 1982, Chapter 2.

Edgerton, S. Y., Jr., Galileo, Florentine 'Disegno,' and the 'Strange Spottednesse' of the Moon. Art Journal, Vol. 44, No. 1, 1984, pp. 225-232.

The Galileo sketches of the moon may be seen at:

This is part of an excellent Galileo website, which I strongly recommend:

Boorstin, D.J., The Discoverers. New York: Random House, 1983, pp. 332-336.

Temple, R., The Genius of China. New York: Simon & Schuster, 1986, pp. 28-30.

Tyndall, J., Light and Electricity: Notes of Two Courses of Lectures Before the Royal Institution of Great Britain. New York: D. Appleton and Co., 1883, pp. 19-20.

Routledge, R., Discoveries and Inventions of the Nineteenth Century. ca. 1890. (Reprinted by Bracken Books, New York, 1989.) pp. 298-301.

See also encyclopedia listings on Roemer.

Howse, D., Greenwich Time and the Discovery of Longitude. New York: Oxford University Press, 1980, Chapter 2.

Sobel, D., Longitude. New York: Walker and Co., 1995.

Kidwell, P.A., Three Women in American Astronomy. American Scientist,Vol. 78, May-June, 1990, pp. 244-251.

Maria Mitchell is well represented on the web. For pictures and more of her history, try these sites:

For more on the many people mentioned here and for much of the subject matter, check the SEARCH and KEYWORDS functions on the Engineswebsite,