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Retrospections Dinner with da Vinci
 
Dinner with da Vinci
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Posted:   08/14/03

Summary: Leonardo da Vinci dreamed of manned flight. While his genius is secured by paintings and inventions, Leonardo's keen observations of nature led him into astronomy. As with most of his work, his insights were highly original and prescient.

Dinner with da Vinci

The Vital Codex of Leonardo

This featured "Dinner with..." series builds on the classic thought experiment: "Which 5 historical figures would you invite to dinner, and how would you seat them?" While the field of astrobiology historically rests on many "shoulders of giants" --too many for one dinner party, the Astrobiology Magazine has selected some initial candidates for our dinner party, and then asks them to introduce their area of expertise in a brief question and answer format.

The answers are their own, as gleaned from some of their most famous, controversial, or seminal contributions to science and technology. In many cases, the selection of commentary is driven by the curiousity to understand these great historical figures as one might imagine them as more modern characters, perhaps joining in on table talk or an informal interview.

Tonight's dinner introduces Leonardo da Vinci. In particular, Leonardo's notebooks--his private writings or codex to himself and ultimately to posterity-- offer brilliant insights into the daily ruminations of an artist, scientist and inventor.

Like most of his contemporaries, when viewed with hindsight, Leonardo had his misconceptions about the universe: the moon had water, the moon had an atmosphere, the moon appeared larger on the Earth's horizon because of distortion of this lunar atmosphere.

But he got many of his speculations right: the moon is reflective, like a mirror, instead of generating its own light. His observations however, had remained unknown to astronomers; Moestlin and Kepler have been credited with the discoveries which they made independently a century later. He regarded himself as the original discoverer of the cause of the ashy color of the new moon ("lumen cinereum").

He maintained that the earth was a globe and not flat.

Like what Leonardo defined as prescience, or seeing the future, his codex was a mixture of science and prescience. Leonardo was both a genius at observing and depicting nature, but also a visionary filled with prescience.


Astrobiology Magazine [AM]: Do you think men someday will fly?

Leonardo: A man with wings large enough and duly connected might learn to overcome the resistance of the air, and by conquering it, succeed in subjugating it and rising above it.

AM: Men will fly with flapping wings, like birds with feathers?

Leonardo: Flying creatures will give their very feathers to support men. It is a feather bed.

AM: [laughing]. Very good. You are an inventor, artist, but have also been quite an observant scientist of nature.

Leonardo: Science is the observation of things possible, whether present or past; prescience is the knowledge of things which may come to pass, though but slowly

AM:
And mathematician?

Leonardo: There is no certainty in sciences where one of the mathematical sciences cannot be applied, or which are not in relation with these mathematics.

Mars plane
Mars airplane design
Credit: NASA


AM: Let's consider some prescience. Will humans travel in space?

Leonardo: Many creatures of land and water will go up among the stars--that is Planets.

AM: Your contemporaries consider the earth a flat disk. Do explorers risk sailing off the edge of the world?

Leonardo: The center of the sphere of waters is the true center of the globe of our world, which is composed of water and earth, having the shape of a sphere.

AM: Your contemporaries also consider the earth as both the center of the solar system, and also the center of the universe. Do you agree?

Leonardo: The earth is not in the center of the Sun's orbit nor at the center of the universe, but in the center of its companion elements, and united with them. And any one standing on the moon, when it and the sun are both beneath us, would see this our earth and the element of water upon it just as we see the moon, and the earth would light it as it lights us.

AM: What causes the ocean tides?

Earth and Moon
Life is possible on Earth because it lies in what is called a habitable zone.
Credit: NASA/JPL


Leonardo: A sea of water is incessantly being drawn off from the surface of the sea. And if you should think that the moon, rising at the Eastern end of the Mediterranean sea must there begin to attract to herself the waters of the sea, it would follow that we must at once see the effect of it at the Eastern end of that sea.

AM: Many have argued about the source of moonlight. Is the moon generating its own light, or merely reflecting from the sun?

Leonardo: I say that as the moon has no light in itself and yet is luminous, it is inevitable but that its light is caused by some other body.

You see here the sun which lights up the moon, a spherical mirror, and all of its surface, which faces the sun is rendered radiant. The moon has no light in itself; but so much of it as faces the sun is illuminated, and of that illumined portion we see so much as faces the earth.

AM: Quite remarkable. Your observation is largely attributed to later astronomers, like Kepler. Modern astronomers also depend critically on an artist's eye, in particular the relation between distance and a star's brightness. This is what gives a two-dimensional view of the sky depth. From the perspective of an artist, what is happening when we view stellar objects on the horizon, or see a very distant object as bright or dim?

Leonardo: The moon is not of itself luminous, but is highly fitted to assimilate the character of light after the manner of a mirror, or of water, or of any other reflecting body; and it grows larger in the East and in the West, like the sun and the other planets.

And the reason is that every luminous body looks larger in proportion as it is remote.

Earth and Moon
Artist eye in dust cloud of exploded star.
Credit: NASA


AM: So even the earth would be a mere speck when viewed from a great distance, looking back?

Leonardo: In my book [codex] I propose to show, how the ocean and the other seas must, by means of the sun, make our world shine with the appearance of a moon, and to the remoter worlds it looks like a star; and this I shall prove.

AM:
Your meditations on perspective, particularly the artist's view of parallax, shows how the distance to an object can be gauged by how far it oscillates or moves when compared with a close object--say, a thumb held close to the eyes, alternately closing one eye or the other, while looking at a distant object. This today is a cosmic yardstick for astrophysicists. But it is still considered almost impossible to determine depth in the star field easily. Modern astronomers consider it such an important measurement, that well over twenty-five different methods are employed to view a star in hopes of also finding its distance. Do you have an artistic proposal like this, to relate brightness to distance?

Leonardo: If you look at the stars, cutting off the rays (as may be done by looking through a very small hole made with the extreme point of a very fine needle, placed so as almost to touch the eye), you will see those stars so minute that it would seem as though nothing could be smaller; it is in fact their great distance which is the reason of their diminution, for many of them are very many times larger than the star which is the earth with water.

Now reflect what this our star must look like at such a distance, and then consider how many stars might be added--both in longitude and latitude--between those stars which are scattered over the darkened sky. But I cannot forbear to condemn many of the ancients, who said that the sun was no larger than it appears.

Earth and Moon
"Some have believed that the moon has some light of its own, but this opinion is false". Leonardo expresses the view that beyond the bright crescent, which is lit by the Sun, the reflection of light from the Earth's seas gives the rest of the Moon a pale light.
Credit: Leonardo's Codex


AM: An important way to measure distances is using the brightness of supernova, or star explosions, to calibrate on a given distance. This is now called in astronomy, the 'standard candle'. But what of the more commonplace twinkling of stars?

Leonardo: If the twinkling of the stars were really in the stars --as it seems to be--that this twinkling appears to be an extension as great as the diameter of the body of the star; therefore, the star being larger than the earth, this motion effected in an instant would be a rapid doubling of the size of the star.

AM:
Remarkably, you are able to conclude so definitively, even though telescopes will not be in use for at least a century after you wrote that in your codex. Have you witnessed an eclipse of the sun?

Leonardo: A method of seeing the sun eclipsed without pain to the eye [is to] take a piece of paper and pierce holes in it with a needle, and look at the sun through these holes.

AM:
Like a pinhole camera. Your Italian countryman, Galileo, developed a serious eye illness from looking at an eclipse, and eventually went blind. If a space traveler were looking back on the earth from the moon, would the earth appear to have phases just as we see the moon from terra firma?

Leonardo: If you were standing on the moon or on a star, our earth would seem to reflect the sun as the moon does.

Earth and Moon
Image of the Earth and Moon taken by Galileo spacecraft.
Credit: NASA


And if you could stand where the moon is, the sun would look to you, as if it were reflected from all the sea that it illuminates by day; and the land amid the water would appear just like the dark spots that are on the moon, which, when looked at from our earth, appears to men the same as our earth would appear to any men who might dwell in the moon.

Again, it might be said that the circle of radiance shown by the moon when it and the sun are both in the West is wholly borrowed from the sun, when it, and the sun, and the eye are situated as is shown above.

AM: It is now proposed and sometimes called the "Gaia hypothesis" that an analogy can be drawn between a living organism, like a human, and various parts of our own biosphere. For instance, roughly that the atmosphere is like the lungs, the oceans like the kidneys, and so forth. What is your view of this proposal?

The doppler effect
Earth as seen by the departing Voyager spacecraft: a tiny, pale blue dot.
Credit: NASA


Leonardo: By the ancients man has been called the world in miniature; and certainly this name is well bestowed, because, inasmuch as man is composed of earth, water, air and fire, his body resembles that of the earth; and as man has in him bones the supports and framework of his flesh, the world has its rocks the supports of the earth; as man has in him a pool of blood in which the lungs rise and fall in breathing, so the body of the earth has its ocean tide which likewise rises and falls every six hours, as if the world breathed; as in that pool of blood veins have their origin, which ramify all over the human body, so likewise the ocean sea fills the body of the earth with infinite springs of water.

AM: The sun, its size, brightness and distance, seems so important to making the earth habitable, including setting the stage for liquid water. What is your artist's opinion on this place in the galaxy?

Leonardo: In the whole universe there is nowhere to be seen a body of greater magnitude and power than the sun; from it descends all vital force.

AM: Your lifetime of work, even scientifically and creatively to a very old age, seems so much larger than life. Any conclusions you can share?

Leonardo: Even if a man were as large as our earth, he would look no bigger than a little star which appears but as a speck in the universe.


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