You will be happy to know that today I’m not going to cram your heads with a lot of facts about astrono … okay, you can stop cheering now. Instead, I’ll discuss just a few of the many astronomers who have had a major influence on the subject. The first three I will discuss are Muggles, the next two are wizards, and the last one is a witch. The witch isn’t known to Muggles, which is not surprising, because the International Statute of Secrecy was in full force by the time she was born, but the others, even the wizards, are so famous that each of them has a crater on the Moon named after him.
Aristarchus (310-230 B.C.E.) was an ancient Greek mathematician and astronomer who was born on the island of Samos. He was a pupil of Strato of Lampsacus, the third head of the Lyceum founded by Aristotle. He is accredited with having invented a widely used type of sundial, and he also wrote a book in which he used mathematics to estimate the relative sizes of the Sun and the Moon. In his work, his mathematics were sound, but one of the observations he used was wrong: he had estimated that the angular distance between the Sun and the Moon at half moon was 87°, when in fact it is 89°50'. As a result, his estimates of the distances were wrong too: he concluded that the Sun was 18 to 20 times as big as the Moon and 18 to 20 times as far away, whereas the correct ratio, both of size and distance, is around 400:1. That said, he did state correctly that Earth is bigger than the Moon, but smaller than the Sun.
He is most famous for having proposed that Earth rotates on its axis, that it and the other planets revolve around the Sun, and that the stars are other suns, possibly with planets revolving around them as well. He reasoned that since the Sun is bigger than the Earth, the Sun should act on Earth more strongly than Earth on the Sun, so the Sun ought to make the Earth revolve around it rather than the other way around. His reasoning was on point, as we now know this action as the force of gravity. As I mentioned a couple weeks ago, his model was condemned as impious by the Stoic philosopher Cleanthes, so he never published it, though we know about it through the writings of Archimedes and the ancient Greek biographer Plutarch. It was almost unanimously rejected in his time, and for some 18 centuries thereafter, in favour of Ptolemy’s geocentric model, until some time after it was proposed by Copernicus.
Nicolaus Copernicus (1473-1543 C.E.) was born in Torun, Poland. He studied liberal arts, including astronomy and astrology, at the University of Cracow from 1491 to 1494, but left the university without obtaining his degree. He then moved to Italy, where he studied canon law at the University of Bologna from 1496 to 1500. His interest in astronomy never waned, however, thanks in large part to the influence of Domenica Maria de Novara, the principal astronomer at the University of Bologna. Copernicus studied medicine and astrology at the University of Padua from 1501 to 1503 and then returned to Poland, where he eventually was employed as a church canon, collecting rent from church-owned land, securing military defenses, overseeing chapter finances, managing the bakery, brewery, and mills, and caring for the medical needs of the other canons.
He worked on astronomy in his spare time. He made many observations, most of them about eclipses, alignments, and conjunctions of the planets and stars. He knew that Aristarchus had long ago proposed that Earth rotates about an axis and that the planets, including Earth, revolve around the Sun, and his observations led him to suspect that this model was correct. In addition, he observed that the calendar then in use had fallen seriously out of alignment with the actual position of the Sun, and he concluded that Earth’s axis was not fixed but itself rotates, a phenomenon now known as the precession of the equinoxes, with a period of 25,772 years. He wrote a six-part book whose title in English is "Six Books Concerning the Revolutions of the Heavenly Orbs" outlining his model, but he never gave Aristarchus any credit for having proposed that same model some 18 centuries earlier. His theory wasn’t generally accepted at the time, largely because it didn’t accurately predict the motion of the planets for the reason discussed in Lesson Seven. He himself wasn’t quite sure that it was correct, so he hesitated to publish it until a pupil of his, who will be discussed later in this lesson, provided the evidence that convinced him to allow it to be published in 1543, the year of his death.
Galileo Galilei (1564-1642) was an Italian mathematician, scientist, and engineer who was born in Pisa. In his teens, he attended the monastery school at Vallombrosa, near Florence, and then entered the University of Pisa to study medicine. However, he became more interested in mathematics, so he quit the university without getting a degree. For a while he gave private lessons in mathematics, and then, in 1588, he applied unsuccessfully to teach mathematics at the University of Bologna, but was successfully hired one year later at the University of Pisa. His rejection of Aristotelian ideas of motion got him fired in 1592, but he got hired again the same year at the University of Padua, where he taught until 1610.
Galileo has been called the father of modern science, because he was the first scientist to perform experiments in order to study the world instead of just reasoning about it. For example, he dropped objects of different weights from the top of the Leaning Tower of Pisa and concluded that light objects and heavy objects fall at the same rate. By experimenting, he discovered the path taken by thrown objects and the distance covered by a falling object in a given amount of time. He studied the strength of materials, invented an early type of thermometer, and made his own telescopes with lenses he ground himself, improving upon them until his latest telescope, which he made in 1610, made objects appear 20 times bigger than they were when viewed with the naked eye. With this telescope, he discovered that the Moon isn’t smooth, that the Sun has spots (looking at the Sun through a telescope eventually blinded him, so remember your safety rules), that Jupiter has four moons, that Saturn has ears (rings), and that Venus has phases.
It was his observation of the phases of Venus that convinced him that Copernicus’s heliocentric model of the solar system was correct. His advocacy of heliocentrism got him in trouble with the Catholic Church, but the pope, who used to be a friend of his, allowed him to write about it as long as he didn’t advocate it. He wrote a book in which his characters debated the question. Overestimating the pope’s tolerance, he had the pope’s opinion that the Earth was the centre of the universe expressed by a man called Simplicio, making the pope so mad that he summoned Galileo to appear before the Inquisition. There he was offered a plea bargain, which he accepted: instead of being imprisoned and tortured, he would merely be put under house arrest for life so long as he publicly recanted his advocacy of Copernicus’s theory. Living in various houses, he continued his work while being cared for by his daughter until he died.
Sir Isaac Newton (1643-1727) was an English physicist and mathematician who was born in Woolsthorpe, Lincolnshire. He had a difficult childhood: before he was born, his father died, and at the age of two he was sent to live with his grandfather by his mother’s second husband. Then, after being widowed a second time, she pulled him out of school to manage her property, but instead of watching the cows, young Newton would read. His mother finally realized her mistake and sent him back to school. After graduating, he enrolled at Cambridge University. All the universities in Europe, even Cambridge, viewed the world according to Aristotle, teaching that the Earth was the centre of the universe. But Newton read the works of the more progressive philosophers, especially René Descartes, from whom he learned that the world was a machine that could be described mathematically, and Pierre Gassendi, who revived the notion that matter was made up of atoms.
Newton became a teacher in Trinity College at Cambridge University in 1667 and a full professor two years later. But he undertook other work as well: to supplement his income, he became Warden of the Mint in 1696. He also achieved many honours. In 1699 the French Academy of Sciences named him one of eight foreign associates, in 1703 he was elected President of the Royal Society, and in 1705 Queen Anne knighted him, which was the first time a scientist was given such an honour.
Newton fully deserved all those honours, for he made many important discoveries. Using a prism, he separated white light into all the colours of the rainbow and then recombined them using another prism. This work led to the practice of spectroscopy, which is used to study the chemical composition of stars and planets and of their atmospheres. Realizing that the edges of lenses acted like prisms, creating colour fringes in the images of these bodies, he invented the reflecting telescope to overcome this problem. Anticipating quantum theory, he proposed that light consists of moving particles. He invented the three laws of motion, which we discussed earlier this year, and proposed that one body could act on another one from a distance. He also studied mathematics all on his own and even went on to invent a new branch of mathematics: calculus, which deals with the rate at which things change, and which he used for many purposes. These included describing the rate at which an object that is at a different temperature from its surroundings gradually assumes the temperature around it, deducing his universal law of gravitation from Kepler’s three laws of planetary motion, and inventing a method of calculating the position of a planet in its orbit at any given time. Isaac Newton is arguably the greatest scientist who ever lived.
Aside from mathematics and physics, he became interested in religion and alchemy. Muggles say that by immersing himself in alchemy, Newton wasted time and effort that could have been more profitably spent in making further scientific discoveries. What they don’t know is that he was a wizard, who used Apparition to travel from place to place quickly for the purpose of gathering information about discoveries made by other scientists, the better to further his own research. Far from wasting his time, he made valuable contributions to alchemy, which you can learn about if you choose to enroll in Alchemy next year.
All his magnificent accomplishments aside, he was not a nice man. He became so furious with anyone who disagreed with him, even his friends, that he would often write terrible things about them and remove all references to their contributions to his work from his books and articles. As President of the Royal Society, he would use his power to punish his enemies and reward his friends – as long as they remained his friends. In the capacity of Warden of the Mint, he sent many counterfeiters to the gallows. The safest way to admire this man of genius was, like a planet being attracted to the Sun, from a distance. He was a prime example of a mad scientist according to both definitions of the word mad: angry and crazy.
George von Rheticus (1514-1576), known to Muggles as Georg Joachim Rheticus, was an Austrian-born astronomer and mathematician. As a mathematician, he worked on his great treatise about triangles, which was published after his death by his pupil Valentin Otto. He studied at Feldkirch, Zurich, and then at the University of Wittenberg, where, upon graduating in 1536, he was appointed to teach mathematics and astronomy. He became so intrigued by Copernicus’s heliocentric model of the solar system that in 1539 he went to Frauenberg (now Frombork, Poland), where he studied with Copernicus for two years as his master’s only pupil. He published a book promoting heliocentrism in 1540 and he encouraged Copernicus to publish his own book on the subject.
But there is a lot more information about von Rheticus than you can find in non-magical sources. He was a wizard whose early education was here at Hogwarts, where he excelled in all his subjects, especially astronomy. It was after graduating from Hogwarts that he returned to the Muggle world to continue his education. During his years as a student at Wittenberg, he invented the telescope that was named after him. You may recall that his telescope could resolve two points of light that were one arcsecond apart. By contrast, Galileo’s best telescope could only resolve two points that were nine arcseconds apart, because, with a magnifying power of 20, it would increase those nine arcseconds to only three arcminutes, which is the smallest angular distance that an observer with average vision can resolve with no optical aid. In addition, Galileo didn’t invent his best telescope until 1610, more than 70 years after von Rheticus invented his. With his telescope, von Rheticus observed the phases of Venus long before Galileo did.
You may also recall that Copernicus wasn’t sufficiently sure of the correctness of his model to be prepared to publish his book about it, but that von Rheticus persuaded him to allow it to be published. How did he manage to do so? He didn’t dare let Copernicus look at Venus through his telescope, because that would have let Copernicus know that he was a wizard. The International Statute of Secrecy hadn’t yet been passed, but there was already enough mistrust of magic among Muggles that Copernicus, already fearing the wrath of the Church if he published his book, would have been further dissuaded for fear of even stronger opposition if it became known that he associated with a wizard. Von Rheticus was aware that there was a geocentric model of the solar system that was compatible with the phases of Venus, as we discussed in Lesson Seven; however, he had enough evidence that this model, too, was false: if Mars revolved around the Earth, its angular size would stay almost constant despite its small epicycles, whereas in fact it appears much smaller when seen near the Sun in the sky than when it is far away. It was this observation that convinced him of the truth of Copernicus’s heliocentric model of the solar system, but he still couldn’t prove it to Copernicus without letting him look at Mars through his telescope.
He finally came up with an observation that Copernicus could make with his naked eye. He had observed that Mars looks not only bigger but also brighter when it appears far away from the Sun in the sky than when it appears near to it. The heliocentric model explains this, but the opposite should be true according to the geocentric model. He drew two explanatory pictures and showed them to Copernicus.
In the heliocentric model, the Mars on top appears farther from the Sun than the Mars on the bottom, and it appears brighter because it’s closer to the Earth and about the same distance from the Sun. In the geocentric model, the Mars on the bottom appears farther from the Sun than the Mars on the top and it appears dimmer because it’s farther from the Sun and about the same distance from the Earth. Over the two years that the two astronomers were together, von Rheticus showed Copernicus that Mars in fact appears brighter when it appears farther from the Sun in the sky, giving Copernicus enough faith in his heliocentric model that he dared to allow his book to be published.
One interesting aspect about von Rheticus’ life is that his father was not only a wizard but a crook in the Muggle world. George’s surname was originally Iserin. His father was caught stealing, and as punishment, the old man was not allowed to use his given name anymore. Through no fault of his own, poor George, too, couldn’t use that surname, so instead he used his mother’s maiden name, becoming George de Porris. Later, he changed his surname again - to von Rheticus - because, at that time in history, most intellectual works were still written in Latin, prompting many intellectual researchers to change their names to Latin ones.
As for von Rheticus’ personality, we do not know for sure. Assuming that the portrait artist captured it well - and you will learn more about magical portraits in Magical Art, should you choose to take it - von Rheticus seemed to like helping others, with the exception of those whom he called “scoundrels.” Sometimes, to prove that you are a good person, he will require you to answer a question about astronomy. Perhaps he developed this attitude because of his own personal relationship with his father, who was quite the scoundrel. But alas, George von Rheticus too became a scoundrel in his later years, but that is a story for another time. Thankfully his crime doesn’t prevent us from appreciating the valuable contribution he made to astronomy.
Doctor Mansour in 2019 at the age of 90.
Ayesha Mansour was born in England to an American father and an English mother on July 30, 1929. She spent most of her childhood in Stamford, Connecticut, but once she came of school age, her parents decided that they wanted her to attend Hogwarts School of Witchcraft and Wizardry, where her mother had received her education. Her father was a Muggle, and her mother wanted first-hand knowledge of the education that her daughter would be getting. Thus they travelled between England and the United States when she was a child, wanting her to be familiar with the UK before sending her off to school alone.
When she was eleven, she was sent to Hogwarts, where she was sorted into Hufflepuff House. She had been nervous about her sorting, but was happy with the house, which she referred to as being her home away from home during her time there. She always had an extremely bubbly and joking personality, something that made her well liked among other students.
Ayesha was never a poor student, but to say that she was a star pupil was a small stretch. However, when she began Astronomy class, something apparently clicked. She fell in love with the subject within the first few weeks and began studying independently with her professor. She constantly craved new knowledge about the field. She stayed with the subject all through her schooling, finishing with an Outstanding grade each year, including her N.E.W.T. This led her to go into research in astronomy as soon as she graduated from Hogwarts, still desiring more knowledge on the subject. She enrolled at Cambridge University, obtaining her Ph.D. in Astronomy in 1953, and then worked to increase her knowledge of magical approaches to astronomy by working with colleagues for a few years before leaving them to pursue her own research. She did so for nearly ten years before making her discovery of the A.M.E.
The wizarding astronomical community is well aware of Dr. Mansour’s work on the A.M.E., but an even more important discovery that she made later is lesser known. As you will learn in Year Three, the Sun’s magic is wild and unpredictable, destroying or altering any magic it hits, but it gets tamed as it passes through the lower levels of the Earth’s atmosphere. Several billion years ago the atmosphere did not tame the Sun’s magic, but the ocean did. From these observations, Dr. Mansour deduced that what tames the Sun’s magic is water - both the water in the ocean and the water vapour that wasn’t originally in the Earth’s atmosphere but that is now.
In 1970 she decided to test her hypothesis by performing an elaborate series of experiments. First, she sent a probe containing an enchanted object into a thermal vent (which, as you will also learn later, releases some of the Earth’s own stored and untamed magic) and found that the enchantment had been destroyed. By sending the probe to places at various distances from the vent, she found that it took about six meters of water to tame its magic. With these initial observations in her back pocket, she decided to take her experiments to the sky. To rise to the top of the layer of the atmosphere that tones down the Sun’s magic, she wore warm clothes and oxygen and other supplies on her back, which she made more portable using the Weight Reduction Charm, and flew in short hops on her broom to the top of a tall mountain. Here she set up a laboratory, which she hid from Muggles using a series of charms. The roof of her laboratory was a transparent dome about a meter thick, which she could fill with water and empty as needed. Then, she tested the effectiveness of various thicknesses of water in her dome by casting the Levitation Charm on one of several objects on a table many times, applying the same amount of concentration and willpower to the best of her ability. As she suspected, when there was no water in the dome, the charm was rather unpredictable, sometimes lifting the wrong object and other times doing nothing at all. When the dome was filled with water, the charm worked a little bit better (though not nearly as well as it did near sea level), confirming her hypothesis that water was the taming agent. As she expected, one meter of water in the dome was only enough to soften the Sun’s magic very slightly.
From her studies at Cambridge, she had also learned about a form of water called heavy water. Each molecule of water has two hydrogen atoms and one oxygen atom. The typical hydrogen atom has only one proton in its nucleus, but about one out of every 6000 has a neutron as well; this form of hydrogen is called deuterium. Water in which both hydrogen atoms are deuterium atoms is about 11% heavier than normal water, hence its name. In 1943, an efficient method of turning normal water into heavy water had been discovered. On a hunch, Dr. Mansour created enough heavy water to fill her dome to a depth of about a millimeter and then repeated her experiment. This time her spell worked just about as well as it did near sea level, leading her to conclude that heavy water in particular is responsible for taming the Sun’s magic as it enters the atmosphere. The effect of this discovery on magical astronomy and Dr. Mansour’s life following it will be discussed in a later year.
I’m happy to see so many of you attending this lesson, the last one of Year One. I hope to see you all in Year Two, when we will be learning many an interesting fact about the Moon. But first, you will need to write a ten-question quiz and a 25-question final exam … okay, I understand that the prospect does not thrill you, but there will also be a more interesting assignment: an essay in which you will interview the portrait of von Rheticus. I will see you all next year!