Great Astronomers: Copernicus
Great Astronomers in Modern English
by Sir Robert S. Ball, 1895 (paraphrased by Leslie Noelani Laurio)
To view the table of contents for the rest of this book, click here.
Nicolaus Copernicus, 1473-1543
"We revolve about the sun like any other planet."
Mikołaj Kopernik -- known to us as Nicolaus Copernicus -- was born in Toruń [or Thorn in German], an old town on the Vistula River in Poland, on February 19, 1473. Since the town was right between Poland and Prussia, with the river making a convenient waterway, it was a busy trading place. Toruń looked different at the time Copernicus was born. The town had walls with watchtowers. Fifteenth century Toruń was such a strategically important place that the German government considered it an important fortress. [Toruń has been considered Polish, Prussian, and German as borders have changed over the centuries, but was Polish in 1473, and is Polish today.]
Copernicus's father was a successful merchant. He died when young Mikołaj was ten. Copernicus didn't come from a noble family, but one of his uncles was a bishop. Not many details of his childhood are available. It seems that Mikołaj was first taught at home, then was sent to grammar school when his uncle took over his education after his father had died, and later was advanced enough to go to the University of Krakow. The education to be had there in those days was probably very primitive, but Copernicus made the most of it. He studied medicine with the intention of becoming a physician. But he already showed some traits of other famous astronomers -- he worked hard at mathematics, and, like Galileo, he was interested in art and actually somewhat successful as a painter. [He was accomplished enough to paint his self-portrait; he probably studied painting while he was in school in Padua, Italy. The well-known historical image of him is a copy of his own self-portrait!]
By the time he was 22 years old [1495], Copernicus had given up on a medical career and decided to focus on science. He already had a job teaching mathematics, and had acquired a bit of renown, which attracted the notice of his uncle, who was a bishop. His uncle suggested that he take holy orders [his uncle had a doctorate in canon law governing the Catholic church], so he did. Soon he was appointed as a canon [a type of clergyman, although he was never ordained as a priest] in the cathedral of Frombork near Gdansk [the "G" is almost silent] near the mouth of the Vistula River.
So, in 1503, Copernicus went to Gdansk. He had a disciplined, somewhat austere spirit, so he resolved to devote his life to serious work. He abandoned ordinary society, and restricted his friendships only to a few very serious, educated companions. He refused to engage in any frivolous, unproductive conversation. He stopped painting. He conducted his regular church duties, collected rents, doctored the sick, and continued his work with astronomy and mathematics. He had the most meager astronomical equipment [telescopes hadn't been invented yet, but he had a quadrant]. He arranged openings in the walls of his house [first a garret in a small farmhouse, but by 1512 he had a room in a tower of the Castle of Warmian Bishops at Lidzbark Warmiński near Olsztyn] so that he could see the stars pass over across the meridian [the latitude line from the north to the south pole]. He was so gifted at practical mechanics that legend says he constructed a canal with some kind of machinery to bring water to the people of Frombork.
[Copernicus had a role in helping to defend Olsztyn castle during the 1520-1521 siege against an army from the Teutonic order.]
The intellectual sleepiness of the Middle Ages was about to be awakened by Copernicus's revolutionary ideas. Interestingly, the time when Copernicus discovered his scheme of the solar system coincided with another great historical event: Copernicus was 19 years old when Columbus discovered the new world.
For centuries, the accepted scientific belief was that the earth was stationary, and that the heavenly bodies that appeared to change position were moving. Ptolemy had said so 1400 years earlier. Ptolemy's theory was mistaken, but it was tied up with so much that was true, and his explanation seemed to fit exactly what men observed with their own eyes. His theory made so much sense that nobody even thought to seriously question it until Copernicus. From time to time, others would vaguely speculate with reasonable indications that it was the sun rather than the earth that was in the center of the solar system with everything else revolving around it. But it's one thing to present a scientific concept, and quite another thing to be able to provide the train of logic from first-hand observation and experimentation with which to prove that concept. Pythagoras told his disciples that it was the sun and not the earth that was the center of the orbits, but there is no evidence that he provided any scientific reasons why that should be so. From the information we have, Pythagoras seems to have related his ideas about heavenly bodies with some wild ideas about the natural world. So he was correct that the sun was the center, but he didn't provide any rational evidence to demonstrate that it was true. But Copernicus convinced anyone who would listen with a detailed train of logical facts that the sun was at the center. Let's take a look at some of his arguments that the solar system is heliocentric [sun-centered] and not geocentric [earth-centered].
Copernicus's first great discovery has something to do with the way the earth turns on its axis. The general daily rotation that makes the stars and other heavenly bodies seem to circle around the sky every twenty four hours prompted Ptolemy to suppose that they actually were moving. In the last chapter we read how Ptolemy considered it strange that a huge object like the celestial sphere surrounding the heavens could move. It meant that the sphere must be moving impossibly fast. Copernicus realized that the daily rising and setting of the sun, moon, and stars could be explained in one of two ways -- either by the celestial sphere rotating and the earth staying still, or by the earth rotating in the opposite direction while the heavens stayed still. He considered both possibilities carefully, like Ptolemy had done. But he came to the opposite conclusion. It seemed to Copernicus that it was more unlikely for the huge sphere to be rotating at high speeds than for the earth to be rotating.
Copernicus showed clearly how the movement of sun, moon, and stars that we see can be explained just as well by the earth rotating as it can by the heavens rotating. He illustrated this by pointing out that people on board a moving ship when the sea is calm perceive that the ship is at rest and the scenery on the shore is moving. If the earth was rotating smoothly, then the people on the earth wouldn't feel its movement. It would seem like the surrounding scenery in the sky was moving.
Copernicus realized that Ptolemy's arguments proving that the earth stayed stationary didn't make sense. It seemed obvious to him that there was no valid reason to refuse to believe that the earth turned. His ability to see this clearly shows his skill in natural philosophy. Ptolemy had speculated that if the earth had been moving, the air would not move with it, and that would cause high winds, blowing all mankind off the planet. Copernicus was convinced that this was a preposterous idea. He thought that the air would travel along with the earth, just as a coat remains around a man even while he walks down the street. Once he had removed this difficulty, he was able to compare both theories side by side to figure out which was responsible for the daily movement of the heavenly bodies.
The truth wasn't difficult to recognize. Which is more likely? That the earth, which might as well be as tiny as a grain of sand in the middle of a huge hollow sphere, is rotating every twenty-four hours, or that the hollow celestial sphere is making an entire rotation around the earth in the opposite direction every twenty-four hours? The first suggestion is much simpler. But Copernicus's solution has even more logic than this. Ptolemy had imagined that all the stars were attached to the surface of the sphere, although he had absolutely no rationale beyond trying to justify his scheme for rotating the huge sphere around the earth. But to Copernicus, a celestial sphere encircling the earth couldn't exist as a physical thing, even though it provided a convenient explanation to account for observable facts with a nice, neat geometrical shape. For one thing, a physical sphere meant that all the stars glued to it would have to be the exact same distance from the earth. This couldn't be proved or disproved, but there was no physical reason why all the stars must be fixed at identical distances from the earth. In fact, it was highly unlikely.
Copernicus must have recognized how problematic it was to come up with the material that such a large sphere would be made out of. And there was another difficulty: what was outside the sphere? Or was it so infinitely thick that it filled the rest of space? And the diameter of such a sphere would have to be thousands of times as big as the earth, meaning that the stars and other heavenly bodies attached to its surface must also be huge. With all of these difficulties, it wasn't hard for him to come to the correct conclusion. After all, which would be harder to rotate -- one single planet turning on its own axis once a day, or a vast sphere with thousands of huge stars that had to travel a thousand times greater the distance of the equator in order to get around the earth every twenty-four hours? The answer seemed so obvious that Copernicus had no choice but to reject Ptolemy's theory that the earth was stationary. Copernicus attributed the daily movement of the heavens to the earth rotating on its axis.
Once he had taken this leap, the difficulties that had to be surmounted in order to explain the huge sphere vanished. It was no longer necessary to suppose that all of the stars were the same distance from the earth. Copernicus realized that some stars could be hundreds of thousands of miles farther away than others. The complicated question of what the sphere was made of no longer existed. The spherical shape of the heavens is only an illusion that we see from our perspective here on the earth, and a convenient point of reference to indicate where individual stars are. Once Copernicus had explained his theory, it was impossible for anyone to deny it if they could grasp the concept and if they were open-minded enough to want to understand it. The idea of a stationary earth was gone forever.
Now that Copernicus had settled the question of whether it was the earth or the celestial heavens that turned, the next step was to consider whether a rotating earth concept might resolve some other difficulties about celestial phenomena. It was already an established idea that the earth was hanging in space with no support. Now Copernicus had shown that it was rotating as it hung there. Since it wasn't attached to anything, might the earth be capable of other movement, too? This was a more challenging question to figure out. It was pretty easy to show how the daily rising and setting of the sun, moon, and stars could be explained by a rotating earth. It was harder to explain the other movements of planets in the heavens that Ptolemy's system had accounted for so beautifully. But if all the planets -- including the earth itself -- were orbiting around the sun every year, that would be harder to prove.
This book isn't detailed enough to explain the geometrical theories that Copernicus depended on. We'll just mention the main ideas. Let's start here: a person who isn't aware that he is on a moving object will look at the world around him moving, and assume it's the rest of the world moving in the opposite direction, not him. A passenger on a boat, for instance, seems to see objects on the river bank moving backwards with the same speed in which his boat is moving forward. This same principle can account for all the movement we see above us -- movement that Ptolemy had explained so brilliantly with his circles within circles. This idea even explains the irregularities of some planets. Mars usually moves from west to east among the stars. But every couple years, it pauses, retraces its steps by moving backwards, pauses again, and then resumes its regular forward movement. Copernicus showed that this effect could just as likely be a result of our viewing the motion of Mars from our moving earth. In the picture below, you can see the paths of Mars and Earth according to Copernicus's theory. The image shows the point in time when the earth comes right in between Mars and the sun. This is when it appears that Mars pauses and goes in the opposite direction -- this is called 'retrograde movement.' Mars is moving in the direction of the arrow, and the earth is traveling in the same direction. But we, who don't feel our own planet moving, seem to see Mars making the opposite movement. It looks like Mars is going in two different directions -- its actual forward movement, and an opposite 'retrograde' movement. If the earth was moving at the same speed Mars is, then the perception of backwards motion would be cancelled out and we'd only seem to see Mars pause among the stars. But Earth is moving faster, so we see the backwards movement going faster than the actual forwards movement -- which makes it look like it's moving backwards. [It's an optical illusion caused by parallax; view it on YouTube.]
Copernicus showed how applying this same idea could explain the characteristics of other planetary movements. Though his theory was resisted at first, it was eventually [after his death] impossible to deny. The world finally accepted that Earth wasn't in the center of the solar system -- Earth wasn't the most supremely important thing in the universe. It was just another one of the planets.
Copernicus was also the first astronomer to give a rational explanation for the change of seasons, as well as trying to figure out other more obscure astronomical phenomena.
He put off publishing his ideas into his old age. He already had an inkling of the opposition he would face when he went public with his discoveries. But his friends finally persuaded him to let the world know, so his book was sent to the printing press. But before the book was available to the public, Copernicus became deathly ill. A published copy of his book was brought to him as he lay on his deathbed in May, 1543. He was able to see it and touch it, but nothing beyond that. He died only a few hours later. He was buried in the cathedral of Frombork where he had spent so much of his life.
[For years, nobody knew for sure where Copernicus was buried in the cathedral -- until very recently. Read about it in this Smithsonian article.]
[Read more about Copernicus at Britannica and this Polish tourism website.]
by Sir Robert S. Ball, 1895 (paraphrased by Leslie Noelani Laurio)
To view the table of contents for the rest of this book, click here.
Nicolaus Copernicus, 1473-1543
"We revolve about the sun like any other planet."
Mikołaj Kopernik -- known to us as Nicolaus Copernicus -- was born in Toruń [or Thorn in German], an old town on the Vistula River in Poland, on February 19, 1473. Since the town was right between Poland and Prussia, with the river making a convenient waterway, it was a busy trading place. Toruń looked different at the time Copernicus was born. The town had walls with watchtowers. Fifteenth century Toruń was such a strategically important place that the German government considered it an important fortress. [Toruń has been considered Polish, Prussian, and German as borders have changed over the centuries, but was Polish in 1473, and is Polish today.]
Copernicus's father was a successful merchant. He died when young Mikołaj was ten. Copernicus didn't come from a noble family, but one of his uncles was a bishop. Not many details of his childhood are available. It seems that Mikołaj was first taught at home, then was sent to grammar school when his uncle took over his education after his father had died, and later was advanced enough to go to the University of Krakow. The education to be had there in those days was probably very primitive, but Copernicus made the most of it. He studied medicine with the intention of becoming a physician. But he already showed some traits of other famous astronomers -- he worked hard at mathematics, and, like Galileo, he was interested in art and actually somewhat successful as a painter. [He was accomplished enough to paint his self-portrait; he probably studied painting while he was in school in Padua, Italy. The well-known historical image of him is a copy of his own self-portrait!]
By the time he was 22 years old [1495], Copernicus had given up on a medical career and decided to focus on science. He already had a job teaching mathematics, and had acquired a bit of renown, which attracted the notice of his uncle, who was a bishop. His uncle suggested that he take holy orders [his uncle had a doctorate in canon law governing the Catholic church], so he did. Soon he was appointed as a canon [a type of clergyman, although he was never ordained as a priest] in the cathedral of Frombork near Gdansk [the "G" is almost silent] near the mouth of the Vistula River.
So, in 1503, Copernicus went to Gdansk. He had a disciplined, somewhat austere spirit, so he resolved to devote his life to serious work. He abandoned ordinary society, and restricted his friendships only to a few very serious, educated companions. He refused to engage in any frivolous, unproductive conversation. He stopped painting. He conducted his regular church duties, collected rents, doctored the sick, and continued his work with astronomy and mathematics. He had the most meager astronomical equipment [telescopes hadn't been invented yet, but he had a quadrant]. He arranged openings in the walls of his house [first a garret in a small farmhouse, but by 1512 he had a room in a tower of the Castle of Warmian Bishops at Lidzbark Warmiński near Olsztyn] so that he could see the stars pass over across the meridian [the latitude line from the north to the south pole]. He was so gifted at practical mechanics that legend says he constructed a canal with some kind of machinery to bring water to the people of Frombork.
[Copernicus had a role in helping to defend Olsztyn castle during the 1520-1521 siege against an army from the Teutonic order.]
The intellectual sleepiness of the Middle Ages was about to be awakened by Copernicus's revolutionary ideas. Interestingly, the time when Copernicus discovered his scheme of the solar system coincided with another great historical event: Copernicus was 19 years old when Columbus discovered the new world.
For centuries, the accepted scientific belief was that the earth was stationary, and that the heavenly bodies that appeared to change position were moving. Ptolemy had said so 1400 years earlier. Ptolemy's theory was mistaken, but it was tied up with so much that was true, and his explanation seemed to fit exactly what men observed with their own eyes. His theory made so much sense that nobody even thought to seriously question it until Copernicus. From time to time, others would vaguely speculate with reasonable indications that it was the sun rather than the earth that was in the center of the solar system with everything else revolving around it. But it's one thing to present a scientific concept, and quite another thing to be able to provide the train of logic from first-hand observation and experimentation with which to prove that concept. Pythagoras told his disciples that it was the sun and not the earth that was the center of the orbits, but there is no evidence that he provided any scientific reasons why that should be so. From the information we have, Pythagoras seems to have related his ideas about heavenly bodies with some wild ideas about the natural world. So he was correct that the sun was the center, but he didn't provide any rational evidence to demonstrate that it was true. But Copernicus convinced anyone who would listen with a detailed train of logical facts that the sun was at the center. Let's take a look at some of his arguments that the solar system is heliocentric [sun-centered] and not geocentric [earth-centered].
Copernicus's first great discovery has something to do with the way the earth turns on its axis. The general daily rotation that makes the stars and other heavenly bodies seem to circle around the sky every twenty four hours prompted Ptolemy to suppose that they actually were moving. In the last chapter we read how Ptolemy considered it strange that a huge object like the celestial sphere surrounding the heavens could move. It meant that the sphere must be moving impossibly fast. Copernicus realized that the daily rising and setting of the sun, moon, and stars could be explained in one of two ways -- either by the celestial sphere rotating and the earth staying still, or by the earth rotating in the opposite direction while the heavens stayed still. He considered both possibilities carefully, like Ptolemy had done. But he came to the opposite conclusion. It seemed to Copernicus that it was more unlikely for the huge sphere to be rotating at high speeds than for the earth to be rotating.
Copernicus showed clearly how the movement of sun, moon, and stars that we see can be explained just as well by the earth rotating as it can by the heavens rotating. He illustrated this by pointing out that people on board a moving ship when the sea is calm perceive that the ship is at rest and the scenery on the shore is moving. If the earth was rotating smoothly, then the people on the earth wouldn't feel its movement. It would seem like the surrounding scenery in the sky was moving.
Copernicus realized that Ptolemy's arguments proving that the earth stayed stationary didn't make sense. It seemed obvious to him that there was no valid reason to refuse to believe that the earth turned. His ability to see this clearly shows his skill in natural philosophy. Ptolemy had speculated that if the earth had been moving, the air would not move with it, and that would cause high winds, blowing all mankind off the planet. Copernicus was convinced that this was a preposterous idea. He thought that the air would travel along with the earth, just as a coat remains around a man even while he walks down the street. Once he had removed this difficulty, he was able to compare both theories side by side to figure out which was responsible for the daily movement of the heavenly bodies.
The truth wasn't difficult to recognize. Which is more likely? That the earth, which might as well be as tiny as a grain of sand in the middle of a huge hollow sphere, is rotating every twenty-four hours, or that the hollow celestial sphere is making an entire rotation around the earth in the opposite direction every twenty-four hours? The first suggestion is much simpler. But Copernicus's solution has even more logic than this. Ptolemy had imagined that all the stars were attached to the surface of the sphere, although he had absolutely no rationale beyond trying to justify his scheme for rotating the huge sphere around the earth. But to Copernicus, a celestial sphere encircling the earth couldn't exist as a physical thing, even though it provided a convenient explanation to account for observable facts with a nice, neat geometrical shape. For one thing, a physical sphere meant that all the stars glued to it would have to be the exact same distance from the earth. This couldn't be proved or disproved, but there was no physical reason why all the stars must be fixed at identical distances from the earth. In fact, it was highly unlikely.
Copernicus must have recognized how problematic it was to come up with the material that such a large sphere would be made out of. And there was another difficulty: what was outside the sphere? Or was it so infinitely thick that it filled the rest of space? And the diameter of such a sphere would have to be thousands of times as big as the earth, meaning that the stars and other heavenly bodies attached to its surface must also be huge. With all of these difficulties, it wasn't hard for him to come to the correct conclusion. After all, which would be harder to rotate -- one single planet turning on its own axis once a day, or a vast sphere with thousands of huge stars that had to travel a thousand times greater the distance of the equator in order to get around the earth every twenty-four hours? The answer seemed so obvious that Copernicus had no choice but to reject Ptolemy's theory that the earth was stationary. Copernicus attributed the daily movement of the heavens to the earth rotating on its axis.
Once he had taken this leap, the difficulties that had to be surmounted in order to explain the huge sphere vanished. It was no longer necessary to suppose that all of the stars were the same distance from the earth. Copernicus realized that some stars could be hundreds of thousands of miles farther away than others. The complicated question of what the sphere was made of no longer existed. The spherical shape of the heavens is only an illusion that we see from our perspective here on the earth, and a convenient point of reference to indicate where individual stars are. Once Copernicus had explained his theory, it was impossible for anyone to deny it if they could grasp the concept and if they were open-minded enough to want to understand it. The idea of a stationary earth was gone forever.
Now that Copernicus had settled the question of whether it was the earth or the celestial heavens that turned, the next step was to consider whether a rotating earth concept might resolve some other difficulties about celestial phenomena. It was already an established idea that the earth was hanging in space with no support. Now Copernicus had shown that it was rotating as it hung there. Since it wasn't attached to anything, might the earth be capable of other movement, too? This was a more challenging question to figure out. It was pretty easy to show how the daily rising and setting of the sun, moon, and stars could be explained by a rotating earth. It was harder to explain the other movements of planets in the heavens that Ptolemy's system had accounted for so beautifully. But if all the planets -- including the earth itself -- were orbiting around the sun every year, that would be harder to prove.
This book isn't detailed enough to explain the geometrical theories that Copernicus depended on. We'll just mention the main ideas. Let's start here: a person who isn't aware that he is on a moving object will look at the world around him moving, and assume it's the rest of the world moving in the opposite direction, not him. A passenger on a boat, for instance, seems to see objects on the river bank moving backwards with the same speed in which his boat is moving forward. This same principle can account for all the movement we see above us -- movement that Ptolemy had explained so brilliantly with his circles within circles. This idea even explains the irregularities of some planets. Mars usually moves from west to east among the stars. But every couple years, it pauses, retraces its steps by moving backwards, pauses again, and then resumes its regular forward movement. Copernicus showed that this effect could just as likely be a result of our viewing the motion of Mars from our moving earth. In the picture below, you can see the paths of Mars and Earth according to Copernicus's theory. The image shows the point in time when the earth comes right in between Mars and the sun. This is when it appears that Mars pauses and goes in the opposite direction -- this is called 'retrograde movement.' Mars is moving in the direction of the arrow, and the earth is traveling in the same direction. But we, who don't feel our own planet moving, seem to see Mars making the opposite movement. It looks like Mars is going in two different directions -- its actual forward movement, and an opposite 'retrograde' movement. If the earth was moving at the same speed Mars is, then the perception of backwards motion would be cancelled out and we'd only seem to see Mars pause among the stars. But Earth is moving faster, so we see the backwards movement going faster than the actual forwards movement -- which makes it look like it's moving backwards. [It's an optical illusion caused by parallax; view it on YouTube.]
Copernicus showed how applying this same idea could explain the characteristics of other planetary movements. Though his theory was resisted at first, it was eventually [after his death] impossible to deny. The world finally accepted that Earth wasn't in the center of the solar system -- Earth wasn't the most supremely important thing in the universe. It was just another one of the planets.
Copernicus was also the first astronomer to give a rational explanation for the change of seasons, as well as trying to figure out other more obscure astronomical phenomena.
He put off publishing his ideas into his old age. He already had an inkling of the opposition he would face when he went public with his discoveries. But his friends finally persuaded him to let the world know, so his book was sent to the printing press. But before the book was available to the public, Copernicus became deathly ill. A published copy of his book was brought to him as he lay on his deathbed in May, 1543. He was able to see it and touch it, but nothing beyond that. He died only a few hours later. He was buried in the cathedral of Frombork where he had spent so much of his life.
[For years, nobody knew for sure where Copernicus was buried in the cathedral -- until very recently. Read about it in this Smithsonian article.]
[Read more about Copernicus at Britannica and this Polish tourism website.]
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