Interdisciplinary Studies in Letters

Interdisciplinary Studies in Letters & Science

Chabot College

Galileo's The Starry Messenger

Pages 23 - 49

Pages

Quote

Interpretation/Comments

23 "Surely a distinguished public service has been rendered...." All about ego, wanting to be remembered? (An Italian trait? :) cf. Dante. He is holding Cosimo (or himself??) up as one worthy of the marble and bronze statues. And more...

"Looking to things even more stable..."

"Thus, turning to the sky, man's wit has inscribed on the familiar and everlasting orbs of most bright stars..."

Beyond the mundane of earthly accomplishments, lies the realm of the heavens. "Wit" here is another reference to (Cosimo's) Galileo's own intellect.

Bright Stars refers to the 5 planets visible with the naked eye, Mercury, Venus, Mars, Jupiter, and Saturn.

24 "In vain did the piety of Augustus... (one of those bodies which the Greeks call "comets" and which the Romans likewise named for their hairy appearance)..." Comets typically last a month or more, but move very quickly as they are brightest when closest to the Sun, and when closest, objects move faster (Kepler's 2nd Law of orbits).

"But we are able, most serene Prince to read Your Highness in the heavens far more accurately and auspiciously..."

"Behold, then, four stars reserved to bear your name..."
Galileo touting his own abilities. Recall his purpose for writing the Prince - to gather fame himself, and a commission to release him from teaching boring classes!

"... at the same time executing with one harmonious accord mighty revolutions every dozen years about the center of the universe; that is, the sun.
What is unique about Jupiter's Moons? The prevailing theory held that the Earth was the center of the Universe, and that all things orbited Earth. To argue that the Earth moved about the Sun was difficult to support, because the concept of gravity did not yet exist as a powerful force extending beyond Earth, nor extending from any other object. Consequently, if one held the Earth did move about the Sun, the moon would not be able to follow. Since the Moon does orbit us, then we could not orbit the Sun.

Logic Aside: If A then B. If not B, then not A.

This second proposition is true, as long as the first is true. Here, the failure in logic is the idea that we would lose the moon (B) if we orbited the Sun (A).

Seeing Jupiter's moons orbit Jupiter, and stay with the planet while it clearly moved against the background stars, meant:

a) Some things did NOT orbit the Earth. Deduction: The Heavens were not exclusively geocentric.

b) Since the "stars" orbiting Jupiter were not lost as Jupiter moved in the sky, perhaps our Moon might not be lost either. Induction: If it works for one, it might work for others.

"For just as these stars, like children worthy of their sire, never leave the side of Jupiter by any appreciable distance..." Galileo is a good writer - the style of praising the ruler is a typical one, and likely required before any of the Prince's underlings would have even passed on the paper.

25 "Jupiter, I say, at the instant of Your Highness' birth, having already emerged from the turbid mists of the horizon and occupied the midst of the heavens, " Jupiter was visible in the sky, both during Cosimo's birth and now. Galileo knew that astrology was still important in the minds of nobles. Jupiter was also considered the most "regal" of planets, given its 12-year orbit, and the reference to Greek/Roman deities, the "king" of the gods.

"But why should I employ mere plausible arguments, when I may prove my conclusion absolutely?" Proof as a scientific concept is crucial to this work. What does it mean to prove a theory? Can you?

27 "Surely it is a great thing to increase the numerous host of fixed stars..." Why was seeing more stars in the heavens important? Science of the day - and "scientists" a.k.a. the church, felt all had been revealed by God, and there was nothing more to "know". This attitude recurred often throughout history of science; in 1900, we thought we understood the atom, only to be fooled by Quantum Mechanics.

28 "In this way one may learn with all the certainty of sense evidence that the moon is not robed..." Why was seeing the moon as imperfect important? "Just like the earth's surface.." (NB "earth not capitalized, but planets were - the Catholic idea of earth being base and sinful, the heavens being perfect.)

"Again, it seems to me a matter of no small importance to have ended the dispute about the Milky Way by making its nature manifest to the very senses as well as to the intellect." It was crucial to have observable proof - there was philosophical speculation since the time of the Greeks, about heliocentrism and the ideas of the heavens. Many argued that the intellectuals were confused. To see, as well as to think, becomes the foundation of current science (observation and theory).

"... after first being illuminated by divine grace" Galileo is religious (and/or shrewd), writing in the style that is accustomed. It would be too much to claim this work as solely his own. Today? A touchdown run, or a home run, or other athletic achievement, often prompts an athelete to praise god.

"... the form and construction of which I shall first briefly explalin, as well as the occasion of its having been devised. Afterwards I shall relate the story of the observations..." This is now considered standard practice - tell what you see briefly (the abstract), tell first HOW you saw what you did, what instruments and techniques you used, and (today) what errors were possible or accuracies expected. This allows the reader to frame their acceptance or rejection of your observations first.

29 "First I prepared a tube..." The telescope has a concave eyepiece and a convex objective lens. He achieved 3x power - equivalent to a simple dime-store monocular. He then made another of about 8x, and finally about 30x. It is the latter that he used to see the moons of Jupiter.

"But forsaking terrestrial observations..." Not really the whole truth - he sold it to the doges of Venice for protection against the pirates -- for a hefty sum. Maintaining that he, not the Flemish inventor, was the originator of the device.

30 "Here it is appropriate... to prepare quite a perfect telescope, which will show all objects bright, distinct, and free from any haziness...."
It is customary to describe the tolerance of the equipment used. He goes on to give a rudimentary test of the seeing power of the scope. (Make one of these for class with a computer?)

He goes on in 30-31 to describe a mathematical, geometric proof of the angular resolution of this telescope. Notice "table of sines" at the top of 31 - even trig was well developed in 1600 (mostly for military reasons; Galileo had developed a military compass for sale.)

31 The Moon:" For greater clarity I distinguish two parts of this surface, a lighter and a darker..."
He is seeing the highlands and lowlands of the lunar surface; the latter also known as "mare" are darker grey because of the higher carbon content; they are "lava lakes" that upwelled from the interior after a particularly significant meteor impact event. He calls the mare "large" or "ancient" spots. The "man in the moon" is seen because of these mare.

He is seeing also craters, which are much smaller, and he claims never to have been seen before.

31 "The things I have seen by which I was enabled to draw this conclusion are as follows." He goes on in 32-33 to describe his observations in much detail, including a sketch. He sees an uneven surface due to the lunar mountains and craters which create shadows, especially noticeable in the crescent phases.

32 "...the boundary which divides the dark part from the light does not extend uniformly... but traces out an uneven, rough, and very wavy line. The Moon's surface is NOT smooth, as should be the case for a heavenly body.

"..the said small spots always agree in having their blackened parts directed towards the sun.." Galileo uses an analogy of seeing dark valleys at sunrise to show that he is seeing depressions in the lunar surface, and bright mountain peaks peeking into the sunlight above.

33 "And on the earth, before the rising of the sun, are not the highest peaks of the mountains illuminated by the sun's rays while the plains remain in shadow?"

34 "Hence if anyone wished to revive the old Pythagorean opinion that the moon is like another earth, its brighter parts might very fitly represent the surface of the land, and its darker regions that of the water" Another comparison with the (imperfect) earth; the analogy that the large lowland dark spots ("mare") were oceans was very common; they aren't water, but carbon-rich materials that appear as lava flood plains, created when the surface of mars was cracked and filled with magma. Note the circular shapes, made by flowing and puddling liquids.

38-39 "But here I forsee that many persons will be assailed by uncertainty and drawn into a grave difficulty..."
"Now since there are many chains of mountains and chasms on the moon.... and since the eye...lies nearly in the plane of their summits, no one need wonder...."

"...that there exists around the body of the moon, just as around earth, a globe of some substance denser than the rest of the aether."
Galileo anticipates an argument - why if the moon is so rough would the *edge* appear so smooth?
He answers by suggesting two causes:

a) the chasms and mountains overlap one another, and "mask" the depressions as seen from our vantage point on Earth.

b) there is a blanket of atmosphere around the moon.

He was right about the first, and wrong about the second.

40 "It remains for me to speak of their dimensions, and to show that the earth's irregularities are far less than those of the moon." Galileo uses geometry to estimate the height of the lunar mountain ranges; his math gave him values of about 4 miles from base to top (about 20,000 feet). The highest indeed are 25,000 feet, and many are between 15,000 and 20,000 feet, so he did quite well.

42- 46 "When the moon is not far from the sun, just before or after new moon, its globe offers itself to view not only on the side where it is adorned with shining horns, but a certain faint light is also seen to mark out the periphery of the dark part with faces away from the sun..."
"For while the moon is between us and the sun (at new moon), there lies before it the entire surface of that hemisphere of the earth which is exposed to the sun and illuminated by vivid rays. The moon receives the light which this reflects..."
Galileo discusses earthshine. He deals with past ideas (the moon's inherent glow, or light from Venus) clearly eliminating them as viable hypotheses.

He then explains clearly how sunlight reflects off of Earth and onto the unlit surface of the moon.

45-46 "The stars, whether fixed or wandering, appear not be enlarged by the telescope in the same proportion as that in which it magnifies other objects." Galileo doesn't say that this effect is due to the distances of the stars - he knew that he couldn't determine those. But he does suggest that the twinkling of stars we see without telescopes are the result of "adventitious and accidental rays".

47 "Now, in addition to stars of the sixth magnitude, a host of other stars are perceived through the telescope which escape the naked eye; these are so numerous as almost to surpass belief." The telescope reveals thousands of unseen stars, too faint to be visible to our eyes.

49 "Third, I have observed the nature and material of the Milky Way. "
"The galaxy is, in fact, nothing but a congeries of innumerable stars grouped together in clusters."

"And what is even more remarkable, the stars which have been called "nebulous" by every astronomer up to this time turn out to be groups of very small stars arranged in a wonderful manner."
The Milky Way Galaxy is seen through the telescope to be much more than a faint, irregular band of whitish light stretching across the sky. Individual stars emerge, and faint cloudy patches ("nebulae") turn out to be globular and galactic clusters.

Pages	Quote	Interpretation/Comments
23	"Surely a distinguished public service has been rendered...."	All about ego, wanting to be remembered? (An Italian trait? :) cf. Dante. He is holding Cosimo (or himself??) up as one worthy of the marble and bronze statues. And more...
	"Looking to things even more stable..." "Thus, turning to the sky, man's wit has inscribed on the familiar and everlasting orbs of most bright stars..."	Beyond the mundane of earthly accomplishments, lies the realm of the heavens. "Wit" here is another reference to (Cosimo's) Galileo's own intellect. Bright Stars refers to the 5 planets visible with the naked eye, Mercury, Venus, Mars, Jupiter, and Saturn.
24	"In vain did the piety of Augustus... (one of those bodies which the Greeks call "comets" and which the Romans likewise named for their hairy appearance)..."	Comets typically last a month or more, but move very quickly as they are brightest when closest to the Sun, and when closest, objects move faster (Kepler's 2nd Law of orbits).
	"But we are able, most serene Prince to read Your Highness in the heavens far more accurately and auspiciously..." "Behold, then, four stars reserved to bear your name..."	Galileo touting his own abilities. Recall his purpose for writing the Prince - to gather fame himself, and a commission to release him from teaching boring classes!
	"... at the same time executing with one harmonious accord mighty revolutions every dozen years about the center of the universe; that is, the sun.	What is unique about Jupiter's Moons? The prevailing theory held that the Earth was the center of the Universe, and that all things orbited Earth. To argue that the Earth moved about the Sun was difficult to support, because the concept of gravity did not yet exist as a powerful force extending beyond Earth, nor extending from any other object. Consequently, if one held the Earth did move about the Sun, the moon would not be able to follow. Since the Moon does orbit us, then we could not orbit the Sun. Logic Aside: If A then B. If not B, then not A. This second proposition is true, as long as the first is true. Here, the failure in logic is the idea that we would lose the moon (B) if we orbited the Sun (A). Seeing Jupiter's moons orbit Jupiter, and stay with the planet while it clearly moved against the background stars, meant: a) Some things did NOT orbit the Earth. Deduction: The Heavens were not exclusively geocentric. b) Since the "stars" orbiting Jupiter were not lost as Jupiter moved in the sky, perhaps our Moon might not be lost either. Induction: If it works for one, it might work for others.
	"For just as these stars, like children worthy of their sire, never leave the side of Jupiter by any appreciable distance..."	Galileo is a good writer - the style of praising the ruler is a typical one, and likely required before any of the Prince's underlings would have even passed on the paper.
25	"Jupiter, I say, at the instant of Your Highness' birth, having already emerged from the turbid mists of the horizon and occupied the midst of the heavens, "	Jupiter was visible in the sky, both during Cosimo's birth and now. Galileo knew that astrology was still important in the minds of nobles. Jupiter was also considered the most "regal" of planets, given its 12-year orbit, and the reference to Greek/Roman deities, the "king" of the gods.
	"But why should I employ mere plausible arguments, when I may prove my conclusion absolutely?"	Proof as a scientific concept is crucial to this work. What does it mean to prove a theory? Can you?
27	"Surely it is a great thing to increase the numerous host of fixed stars..."	Why was seeing more stars in the heavens important? Science of the day - and "scientists" a.k.a. the church, felt all had been revealed by God, and there was nothing more to "know". This attitude recurred often throughout history of science; in 1900, we thought we understood the atom, only to be fooled by Quantum Mechanics.
28	"In this way one may learn with all the certainty of sense evidence that the moon is not robed..."	Why was seeing the moon as imperfect important? "Just like the earth's surface.." (NB "earth not capitalized, but planets were - the Catholic idea of earth being base and sinful, the heavens being perfect.)
	"Again, it seems to me a matter of no small importance to have ended the dispute about the Milky Way by making its nature manifest to the very senses as well as to the intellect."	It was crucial to have observable proof - there was philosophical speculation since the time of the Greeks, about heliocentrism and the ideas of the heavens. Many argued that the intellectuals were confused. To see, as well as to think, becomes the foundation of current science (observation and theory).
	"... after first being illuminated by divine grace"	Galileo is religious (and/or shrewd), writing in the style that is accustomed. It would be too much to claim this work as solely his own. Today? A touchdown run, or a home run, or other athletic achievement, often prompts an athelete to praise god.
	"... the form and construction of which I shall first briefly explalin, as well as the occasion of its having been devised. Afterwards I shall relate the story of the observations..."	This is now considered standard practice - tell what you see briefly (the abstract), tell first HOW you saw what you did, what instruments and techniques you used, and (today) what errors were possible or accuracies expected. This allows the reader to frame their acceptance or rejection of your observations first.
29	"First I prepared a tube..."	The telescope has a concave eyepiece and a convex objective lens. He achieved 3x power - equivalent to a simple dime-store monocular. He then made another of about 8x, and finally about 30x. It is the latter that he used to see the moons of Jupiter.
	"But forsaking terrestrial observations..."	Not really the whole truth - he sold it to the doges of Venice for protection against the pirates -- for a hefty sum. Maintaining that he, not the Flemish inventor, was the originator of the device.
30	"Here it is appropriate... to prepare quite a perfect telescope, which will show all objects bright, distinct, and free from any haziness...."	It is customary to describe the tolerance of the equipment used. He goes on to give a rudimentary test of the seeing power of the scope. (Make one of these for class with a computer?) He goes on in 30-31 to describe a mathematical, geometric proof of the angular resolution of this telescope. Notice "table of sines" at the top of 31 - even trig was well developed in 1600 (mostly for military reasons; Galileo had developed a military compass for sale.)
31	The Moon:" For greater clarity I distinguish two parts of this surface, a lighter and a darker..."	He is seeing the highlands and lowlands of the lunar surface; the latter also known as "mare" are darker grey because of the higher carbon content; they are "lava lakes" that upwelled from the interior after a particularly significant meteor impact event. He calls the mare "large" or "ancient" spots. The "man in the moon" is seen because of these mare. He is seeing also craters, which are much smaller, and he claims never to have been seen before.
31	"The things I have seen by which I was enabled to draw this conclusion are as follows."	He goes on in 32-33 to describe his observations in much detail, including a sketch. He sees an uneven surface due to the lunar mountains and craters which create shadows, especially noticeable in the crescent phases.
32	"...the boundary which divides the dark part from the light does not extend uniformly... but traces out an uneven, rough, and very wavy line.	The Moon's surface is NOT smooth, as should be the case for a heavenly body.
	"..the said small spots always agree in having their blackened parts directed towards the sun.."	Galileo uses an analogy of seeing dark valleys at sunrise to show that he is seeing depressions in the lunar surface, and bright mountain peaks peeking into the sunlight above.
33	"And on the earth, before the rising of the sun, are not the highest peaks of the mountains illuminated by the sun's rays while the plains remain in shadow?"
34	"Hence if anyone wished to revive the old Pythagorean opinion that the moon is like another earth, its brighter parts might very fitly represent the surface of the land, and its darker regions that of the water"	Another comparison with the (imperfect) earth; the analogy that the large lowland dark spots ("mare") were oceans was very common; they aren't water, but carbon-rich materials that appear as lava flood plains, created when the surface of mars was cracked and filled with magma. Note the circular shapes, made by flowing and puddling liquids.
38-39	"But here I forsee that many persons will be assailed by uncertainty and drawn into a grave difficulty..." "Now since there are many chains of mountains and chasms on the moon.... and since the eye...lies nearly in the plane of their summits, no one need wonder...." "...that there exists around the body of the moon, just as around earth, a globe of some substance denser than the rest of the aether."	Galileo anticipates an argument - why if the moon is so rough would the edge appear so smooth? He answers by suggesting two causes: a) the chasms and mountains overlap one another, and "mask" the depressions as seen from our vantage point on Earth. b) there is a blanket of atmosphere around the moon. He was right about the first, and wrong about the second.
40	"It remains for me to speak of their dimensions, and to show that the earth's irregularities are far less than those of the moon."	Galileo uses geometry to estimate the height of the lunar mountain ranges; his math gave him values of about 4 miles from base to top (about 20,000 feet). The highest indeed are 25,000 feet, and many are between 15,000 and 20,000 feet, so he did quite well.
42- 46	"When the moon is not far from the sun, just before or after new moon, its globe offers itself to view not only on the side where it is adorned with shining horns, but a certain faint light is also seen to mark out the periphery of the dark part with faces away from the sun..." "For while the moon is between us and the sun (at new moon), there lies before it the entire surface of that hemisphere of the earth which is exposed to the sun and illuminated by vivid rays. The moon receives the light which this reflects..."	Galileo discusses earthshine. He deals with past ideas (the moon's inherent glow, or light from Venus) clearly eliminating them as viable hypotheses. He then explains clearly how sunlight reflects off of Earth and onto the unlit surface of the moon.
45-46	"The stars, whether fixed or wandering, appear not be enlarged by the telescope in the same proportion as that in which it magnifies other objects."	Galileo doesn't say that this effect is due to the distances of the stars - he knew that he couldn't determine those. But he does suggest that the twinkling of stars we see without telescopes are the result of "adventitious and accidental rays".
47	"Now, in addition to stars of the sixth magnitude, a host of other stars are perceived through the telescope which escape the naked eye; these are so numerous as almost to surpass belief."	The telescope reveals thousands of unseen stars, too faint to be visible to our eyes.
49	"Third, I have observed the nature and material of the Milky Way. " "The galaxy is, in fact, nothing but a congeries of innumerable stars grouped together in clusters." "And what is even more remarkable, the stars which have been called "nebulous" by every astronomer up to this time turn out to be groups of very small stars arranged in a wonderful manner."	The Milky Way Galaxy is seen through the telescope to be much more than a faint, irregular band of whitish light stretching across the sky. Individual stars emerge, and faint cloudy patches ("nebulae") turn out to be globular and galactic clusters.