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Danish astronomer Tycho Brahe made the most accurate celestial observations of his time and challenged the prevailing belief in how the universe was organized. And while most people may think of scientists as stodgy academic types, Brahe's flamboyant lifestyle and ignominious death would have made some of today's wild celebrities look like choirboys.

Born in Denmark in 1546, Brahe's parents were members of the nobility. He was raised by his wealthy uncle and attended universities in Copenhagen and Leipzig. Though he studied arts subjects with the intention of becoming a lawyer, Brahe chose instead to pursue astronomy.

In 1566, 20-year-old Brahe fought a fellow student in a duel over who was the better mathematician. As a result, he lost a large chunk of his nose. "It's the least desirable dueling scar. A dueling scar is a mark of aristocratic courage, but that's if you have a little line on your cheek or a little scratch on your forehead," John Robert Christianson, a Professor Emeritus of History at Luther College and the author of On Tycho's Island (Cambridge University Press, 2000) and Tycho Brahe and the Measure of the Heavens (Reaktion Books, 2020), told our sister publication All About History magazine. "Having half of your nose whacked off is not very appealing so he had to wear a prosthesis his whole life long. That was a source of ridicule on the part of his astronomical opponents."
Related:

Famous astronomers: How these scientists shaped astronomy
Tycho Brahe pronunciation

When Brahe was born, his Danish name was Tyge Otteson Brahe. However, he adopted a Latinized form, Tycho Brahe, when he was about 15 years old. There is not much consensus about how the name is pronounced in English. Some say his first name is "tee-ko"; others say "tie-ko." His last name is pronounced either "brah," "bra-hay" or "bra-hee." He is sometimes referred to only by his first name, as in Tycho Crater on , the Tycho Deep Space capsule and Tycho's Supernova Remnant.

Contribution to astronomy

Despite his colorful life, Brahe contributed a great deal to the field of . At the time, astronomers held to the idea that the heavens were composed of separate individual spheres, with everything revolving around Earth.

In 1572, Brahe observed a supernova in the constellation of Cassiopeia. Brighter than , the new star remained visible for a year and a half. In 1577, he observed a . Current theory taught that both were disturbances in the atmosphere. However, Brahe's precise measurements revealed differently. He proved that the never changed with regard to the surrounding and that the comet orbited beyond the path of the moon, contradicting the idea that the heavens never changed.

"Upon learning that Tycho intended to leave Denmark [in 1575] in order to pursue his interests in studying the universe, King Frederick granted him the island of Hven, and helped finance the building of his observatory there," Associate Professor of History at Swansea University and author of Bearing the Heavens: Tycho Brahe and the Astronomical Community of the Late Sixteenth Century (Cambridge University Press, 2007) Dr Adam Mosley told All About History magazine in an interview. "Tycho served as a kind of consultant to the royal court, commenting on and explaining unusual natural phenomena, such as the great comet of 1577, and he produced horoscopes for the royal family."

At his observatory, Brahe kept meticulous observations of the heavens. While most astronomers only focused on observing heavenly bodies at specific, unusual points in their orbits, Brahe intently tracked them in their entire visible orbit across the sky, creating the most precise observations made at the time. Some of his measurements were accurate to half an arc minute, which is especially admirable given that they were all made before the advent of the telescope.

Although Brahe's observations revealed the flaws of the current system, he did not embrace Nicolaus Copernicus' newly proposed sun-centered model. Instead, he offered a model that combined the two, setting the moon and sun in orbit around even as the other five known planets circled . The model became popular among those who wanted to leave the older view behind but weren't ready to embrace the idea of the sun at the center of the solar system.

(Image credit: Fototeca Gilardi/Getty Images)

Related: Geocentric model: The Earth-centered view of the universe

"In Tycho Brahe's geo heliocentric system, the planets moved around the sun, and the stars, sun, and moon moved around Earth, with Earth at the center of the universe," explained Mosley. "This geo heliocentric system was thought by Tycho Brahe, and by some astronomers and philosophers in the seventeenth century, to overcome some of the problems with the two alternative systems."

According to Rice University's Galileo Project, "Tycho Brahe's contributions to astronomy were enormous." In addition to his observations, he also designed and built instruments, periodically calibrating them and checking their accuracy. "He thus revolutionized astronomical instrumentation."

Another of Tycho's most impressive accomplishments was his use of statistical information. "This was his great contribution - he basically invented the concept of data. He was the first person to repeat an observation or experiment in order to verify it," stated Christianson. The vast body of data collected by Tycho not only helped him in his work but also served the astronomers who followed him.

(Image credit: myLoupe/Universal Images Group via Getty Images)

Tycho's Observatory

On the island of Hven, Tycho's scientific sanctuary was built and named Uraniborg. "You can still look out the window of the king's apartment at Kronborg Castle and you're looking right at that island," Christianson told All About History. "That was how the king chose that island. He gave it to Tycho Brahe and said: "I want you to continue to pursue your studies because you will bring fame to the Kingdom of Denmark. I want you to do it on that island within sight of the new castle that I'm building here. That will be the showplace of the realm and I want your little island to be part of that showplace." When monarchs built palaces at that time, you had to have a chamber of wonders - a display of marvelous things that are exemplars of your royal power and King Frederick II wanted Tycho Brahe to build that little island of wonders."

The elaborate Renaissance villa on Hven had towers on the outer sides which were part of his observatory and housed his large scientific instruments. Panels in the roofs of these towers could be removed to reveal the sky to those inside. At Uraniborg, Tycho carried out his observations for around 20 years. He made a variety of new instruments to help him in his work, ran his own printing press and educated and trained upcoming astronomers from around Europe. The island of Hven now has a Tycho Brahe museum where visitors can also see the ruins of his famous observatory.

How Kepler got his start

Brahe's precise measurements laid the foundation for a new understanding of the motion of the planets. German astronomer Johannes Kepler contacted him at the end of the 16th century in an effort to obtain copies of the Danish astronomer's research. Brahe countered with a suggestion that Kepler could work as his assistant, helping him to compile his data.

By this time, Brahe was based in Prague at the court of Holy Roman Emperor Rudolf II and worked as the Imperial Mathematician assisted by Kepler. Their relationship was often a fraught one, with Kepler wanting to use Brahe's data to support Copernicus' theory of heliocentrism, rather than help Brahe refine his own model of the universe. However, the two men continued to collaborate despite their differences.

Brahe suggested that Kepler work on solving the dilemma that plagued astronomers. Because of its orbit, Mars appears to occasionally move backward across the sky, causing many astronomers to suggest epicycles, tiny circles within their orbit. Even Copernicus' suggestion that the planets orbited the sun in circles could not account for the red planet's strange motion.

After his death, the body of data that Brahe had accumulated during his lifetime proved to be particularly valuable, both intellectually, and importantly for his children, financially. "The Emperor offered to buy all of Tycho's instruments and his data but he was short on cash and so he made a down payment. For the rest of the lives of Tycho Brahe's children he continued, annually, to pay them the amount of the purchase," said Christianson. As the succeeding Imperial Mathematician, Kepler used the data purchased by the Emperor to further his own career and make a name for himself.

Kepler, using Brahe's detailed observations, realized that the planets moved around the sun not in circles but in stretched-out circles known as ellipses. However, the problem took him almost a decade to solve, and Kepler didn't publish it until well after Brahe's death.

A mysterious death

Brahe died in 1601 at the age of 54. While attending a banquet, societal customs did not allow him to excuse himself before his host. Brahe had drunk excessively but refused to leave to use the bathroom. It is thought that this exacerbated some kind of bladder infection the astronomer was suffering from and as a result, he developed uremia. According to Kepler in his account of his mentor's death, Brahe died five days after the banquet.

However, scientists who opened Brahe's grave in 1901 to mark the 300th anniversary of his death claimed to find mercury in his remains, fueling rumors that the astronomer was poisoned. Some even accused a jealous Johannes Kepler of the crime.

Brahe's body was exhumed again in 2010. Tests on his bones and beard hairs showed that mercury concentrations in his body were not high enough to have killed him.

"In fact, chemical analyses of the bones indicate that Tycho Brahe was not exposed to an abnormally high mercury load in the last five to ten years of his life," researcher Kaare Lund Rasmussen, an associate professor of chemistry at the University of Southern Denmark who analyzed mercury levels in Brahe's beard and bones, said in a statement.

However, further research revealed that the astronomer was exposed to high levels of gold in his lifetime. "We found traces of gold in Tycho Brahe's hair, and we can establish that he was exposed to gold while these hairs were still on his body," Rasmussen said in a 2016 statement.

"It may have been the cutlery and plates of gold, or maybe the wine he drank contained gold leaf. It's also possible that he concocted and consumed elixirs containing gold, or that he worked with alchemy,"

Researchers also found that greenish stains around the nasal areas of Brahe's corpse contained traces of copper and zinc, indicating that his fake nose was made of brass and not silver or gold, as many had believed.

"When we exhumed the body in 2010, we took a small bone sample from the nose so that we could examine its chemical composition," project leader Jens Vellev, an archaeologist at Aarhus University in Denmark, said the same statement. "Surprisingly, our analyses revealed that the prosthesis was not made of precious metals, as was previously supposed ... So Tycho Brahe's famous 'silver nose' wasn't made of silver after all."

Additional resources

To learn more about Tycho Brahe's supernova, NASA has some useful resources. you Or, if you want to take a trip to Brahe's observatory on the island of Hven, information can be found about the Tycho Brahe museum there on their official website.

Bibliography

Christianson, J. R. (2000). On Tycho's Island. Cambridge University Press.

Christianson, J. R. (2020). Tycho Brahe and the Measure of the Heavens. Reaktion Books.

Mosley, A. (2007). Bearing the Heavens: Tycho Brahe and the Astronomical Community of the Late Sixteenth Century. Cambridge University Press.

O'Connor, J.J. and Robertson, E.F. (2003). Tycho Brahe. Retrieved from https://mathshistory.st-andrews.ac.uk/Biographies/Brahe/

Smith, Y. (2019, Oct 23). The Tycho Supernova: Death of a Star. NASA. Retrieved from https://www.nasa.gov/image-feature/the-tycho-supernova-death-of-a-star

Tycho Brahe (1546-1601) (1995). Retrieved from http://galileo.rice.edu/sci/brahe.html

The Astronomers Tycho Brahe and Johannes Kepler. Retrieved from https://chandra.harvard.edu/edu/formal/icecore/The_Astronomers_Tycho_Brahe_and_Johannes_Kepler.pdf

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Tycho Brahe was a pioneering Danish astronomer from the 16th century whose data collection and discoveries changed the way scientists looked at the skies.

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Italian astronomer Galileo Galilei provided a number of scientific insights that laid the foundation for future scientists. His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time - that all things revolved around the Earth.

[See also our overview of Famous Astronomers and great scientists from many fields who have contributed to the rich history of discoveries in astronomy.]

Galileo's experiments

The Ancient Greek philosopher, Aristotle, taught that heavier objects fall faster than lighter ones, a belief still held in Galileo's lifetime. But Galileo wasn't convinced. Experimenting with balls of different sizes and weights, he rolled them down ramps with various inclinations. His experiments revealed that all of the balls boasted the same acceleration independent of their mass. He also demonstrated that objects thrown in the air travel along a parabola.

At the same time, Galileo worked with pendulums. In his life, accurate timekeeping was virtually nonexistent. Galileo observed, however, that the steady motion of a pendulum could improve this. In 1602, he determined that the time it takes a pendulum to swing back and forth does not depend on the arc of the swing. Near the end of his lifetime, Galileo designed the first pendulum clock.

Galileo's telescope

Galileo is often incorrectly credited with the creation of a telescope. ( Hans Lippershey applied for the first patent in 1608, but others may have beaten him to the actual invention.) Instead, he significantly improved upon them. In 1609, he first learned of the existence of the spyglass, which excited him. He began to experiment with telescope-making, going so far as to grind and polish his own lenses. His telescope allowed him to see with a magnification of eight or nine times. In comparison, spyglasses of the day only provided a magnification of three.

It wasn't long before Galileo turned his telescope to the heavens. He was the first to see craters on the moon, he discovered sunspots, and he tracked the phases of Venus. The rings of Saturn puzzled him, appearing as lobes and vanishing when they were edge-on - but he saw them, which was more than can be said of his contemporaries.

Of all of his telescope discoveries, he is perhaps most known for his discovery of the four most massive moons of Jupiter, now known as the Galilean moons: Io, Ganymede, Europa and Callisto. When NASA sent a mission to Jupiter in the 1990s, it was called Galileo in honor of the famed astronomer.

In his book " Sidereus Nuncius" ("Starry Messenger"), published in 1610, Galileo wrote:

"On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavens through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, namely that three little stars, small but very bright, were near the planet; and although I believed them to belong to a number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude . . . When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night."

"I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury around the Sun; which was at length established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter."

Galileo may also have made the first recorded studies of the planet Neptune, though he didn't recognize it as a planet. While observing Jupiter's moons in 1612 and 1613, he recorded a nearby star whose position is not found in any modern catalogues.

"It has been known for several decades that this unknown star was actually the planet Neptune," University of Melbourne physicist David Jamieson told Space.com. "Computer simulations show the precision of his observations revealing that Neptune would have looked just like a faint star almost exactly where Galileo observed it."

Copernican system

In Galileo's lifetime, all celestial bodies were thought to orbit the Earth. Supported by the Catholic Church, teaching opposite of this system was declared heresy in 1615.

Galileo, however, did not agree. His research - including his observations of the phases of Venus and the fact that Jupiter boasted moons that didn't orbit Earth - supported the Copernican system, which (correctly) stated that the Earth and other planets circle the sun.

In 1616, he was summoned to Rome and warned not to teach or write about this controversial theory. But in 1632, believing that he could write on the subject if he treated it as a mathematical proposition, he published work on the Copernican system. He was found guilty of heresy, and was placed under house arrest for the remaining nine years of his life.

Galileo quotes

"And yet it moves."

"I have never met a man so ignorant that I couldn't learn something from him."

"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use."

"You cannot teach a man anything, you can only help him find it within himself."

"It is a beautiful and delightful sight to behold the body of the Moon."

"Wine is sunlight, held together by water."

- Find other quotes at GoodReads.com.
Additional resources

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Galileo Galilei: Biography, Inventions & Other Facts

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Italian astronomer Galileo Galilei provided a number of scientific insights that laid the foundation for future scientists. His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time - that all things revolved around the Earth.

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Lived 1571 to 1630.
Johannes Kepler played a key role in the profound changes in human thinking that took place during the the scientific revolution. In Kepler's lifetime:

religion clashed with religion

religion clashed with science

the old ideas of Ptolomy and Aristotle clashed with the new discoveries of Copernicus and Galileo

the superstition of astrology clashed with the science of astronomy

Kepler reflected the times he lived in. Seen through modern eyes, he had somewhat contradictory ideas. He was:

an unorthodox Protestant

a follower of Copernicus and Galileo

a brilliant mathematician and scientist who discovered that the solar system's planets follow elliptical paths, not circular paths

an astrologer, whose horoscopes were sought out as among the best available

Such contradictions were not unusual during the scientific revolution. Isaac Newton, who lived in a later time than Kepler (1643 to 1727) did not work in the way a modern scientist would. Also a Protestant with unorthodox views, Newton spent more time investigating the true meaning of the Bible's words and on the pseudoscience of alchemy than he did on mathematics or physics!

Johannes Kepler's Early Life and Education

Johannes Kepler was born on December 27, 1571, in the town of Weil der Stadt, which then lay in the Holy Roman Empire, and is now in Germany.

His mother, Katharina Guldenmann, was a herbalist who helped run an inn owned by her father. When Johannes was about five years old, his father, Heinrich Kepler, was killed in Holland fighting as a mercenary.

Physically Damaged, Intellectually Strong
The young Johannes Kepler was prone to ill-health. His hands were crippled and his eyesight permanently impaired by smallpox. Despite these difficulties, guests at his grandfathers' inn were astonished at his ability to solve any problem they brought him involving numbers.

His herbalist mother, Katharina, tried to convey her love of the natural world to her son. She made a point of taking him out at night to show him interesting things in the heavens, including a comet and a lunar eclipse.

In doing so, she set her son on a course which would eventually transform our understanding of the solar system and the universe.

School
Kepler was formally schooled in Latin - the language of academics, the legal profession and churchmen throughout Europe - and then attended the Protestant Seminary of Maulbronn, because he wished to become a Protestant minister.

Completing his studies at Maulbronn, he moved on to the University of Tübingen. There, although he took courses in Theology, Greek, Hebrew, and Philosophy, it was in Mathematics that he stood out.

He was one of the few students deemed intellectually and mathematically capable of being taught the work of Nicolaus Copernicus. Kepler decided that Copernicus's heliocentric hypothesis, that the sun lay at the center of the solar system, was correct.

In 1594, aged 23, Kepler became a lecturer in astronomy and mathematics at the Protestant School in the city of Graz, Austria.

Kepler Discovers the Truth about Planets' Orbits

Kepler thought Copernicus's heliocentric view of the solar system was right.

His own belief was that the sun exerted a force on the planets orbiting it.

In 1596, at the age of 25, he published a book - Mystery of the Cosmos. His book explained why, logically, the sun lay at the center of the solar system.

Kepler noted that Mercury and Venus always seem to be close to the sun, unlike Mars, Jupiter and Saturn. This is because Mercury and Venus's orbits are closer to the sun than Earth's. Kepler said that if the sun and all the planets orbited Earth, there is no reason why Mercury and Venus should always be near the sun.

Kepler Sees the Hand of God
Including Earth, there were six known planets. (Uranus, Neptune, and Pluto, had not been discovered in Kepler's era.)

Looking for evidence of 'God the mathematician,' Kepler was able to justify six planets and their distances from the sun in terms of the five Platonic solids. These are the five highly symmetrical, regular, 3D solids whose perfect symmetry allows them to be used as dice.

Remarkably, looked at in the way Kepler did, his Platonic solids theory produced a close fit to the planet-to-sun distances that Copernicus had found.

Kepler Seeks Better Data
Thrilled that he had found evidence of the hand of God in the solar system's design, Kepler now sought better data.

He hoped that more accurate astronomical observations would prove his theory.

By great good fortune, at exactly the same time as Kepler sought better data, one of Europe's foremost astronomers, Tycho Brahe, was hoping to recruit an assistant who could carry out astronomy calculations.

The two started working together, although it was not a match made in heaven! Tycho was notoriously quarrelsome - he had worn a metal nose ever since he lost his real nose in a duel fought over the merits of a particular mathematics formula!

Tycho Brahe's Data
Early in the year 1600, Kepler moved from Graz to the town of Benatek, which today is in the Czech Republic. There Tycho, who was the imperial mathematician to Holy Roman Emperor Rudolph II, had an observatory.

Tycho gave Kepler access to some of his Mars observations, but not all. Then the pair fell out and Kepler spent some time in Prague, then Graz, before they resolved their differences and got together again.

During 1601, Kepler carried out calculations of planet movements for Tycho. In October 1601, Tycho died. Kepler replaced him as the imperial mathematician.

Kepler now had unrestricted access to all of Tycho's astronomical data. With an incredible amount of hard work he began to deduce the laws that govern the movements of the planets. The first law he found is now called his second law!

Kepler's Second Law - The Law of Areas

From Tycho's very accurate observations, Kepler discovered that Mars does not move in a perfect circle around the sun.

This was scandalous! Everyone 'knew' that heavenly bodies were perfect, traveling along a path whose shape was perfect - the circle.

It took a long time before people came to terms with Kepler's shocking discovery and started to believe it. All the more so because the planets' orbits are actually very close to circular.

It is a tribute to both the precision of Tycho's observations and Kepler's calculating prowess that Kepler was ever able to discover the truth.

Kepler found Mars was moving in an oval-like orbit and that sometimes it was closer to the sun than at others. When close to the sun, it moved faster than when it was farther away.

In 1602, Kepler deduced what came to be called his second law: a line drawn from planet to sun sweeps out equal areas in equal times.

Kepler's First Law - The Law of Orbits
Kepler tried to figure out the mathematical shape of Mars's orbit. After about 40 misses, in 1605, he got it right. Mars follows an elliptical path around the sun.

And now he formulated what would become Kepler's first law: planets orbit the sun in ellipses, with the sun at one focus.

Kepler's Third Law - The Law of Periods
Kepler never gave up his idea that regular polygons determine the orbits of the planets. As a fortunate result of this wrong thinking, he continued calculating and theorizing.

In 1618 his continuing research led to his third law of planetary motion:

The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit.

Restated crudely, this law means that if we square the time it takes a planet to complete one orbit around the sun, we'll find it's proportional to the planet's distance from the sun cubed.

Even more crudely: the farther a planet is from the sun, the slower it moves along its orbital path.

Summing up Kepler's Laws and their Significance

In a 17 year period, when he was aged between 30 and 47, Kepler took Copernicus's mathematically flawed heliocentric solar system by the scruff of the neck and put it on a rock-solid mathematical footing.

During his own lifetime, the huge significance of his work won little or no recognition.

Later, however, his work provided the platform for Isaac Newton to discover the law of universal gravitation. When Newton (perhaps with double meaning) said that if he had seen further, it was by standing on the shoulders of giants, there can be no doubt that Johannes Kepler was one of the giants.

More of Kepler's Achievements

The Tides

Although he greatly admired Galileo's work, Kepler disagreed with him about the cause of tides on Earth. Galileo believed they were caused by the earth spinning. Kepler, correctly, identified that they were caused by the moon.

Kepler wrote, about a 'magnetic force' which we would today call the force of gravity.

Optics

Kepler made important discoveries in optics.

Light Intensity
In 1604, Kepler discovered the inverse square law of light intensity.

The consequence of this law is, for example, that while Jupiter is about five times farther than Earth from the sun, each square meter of Jupiter receives only one-twenty-fifth of the sun's energy compared with a square meter on Earth.

When Newton, guided by Kepler's Third Law, discovered the law of universal gravitation, he found that gravity also follows an inverse square law. So, if you triple your distance from the sun, the force of gravity you feel is divided by nine.

Everything is Upside Down
It was Kepler who discovered that the lenses in our eyes invert images. This means images on our retinas are upside down. Kepler correctly concluded that the inverted image is corrected by our brains.

Designing a Better Telescope
In 1610 Kepler was excited by news from Italy, where Galileo had discovered four moons orbiting Jupiter.

In 1611 Kepler turned his attention to Galileo's telescope design, improving it by using two convex lenses. This allowed higher magnifications. Kepler's design is now the standard design for refracting telescopes.

Kepler's 'Last Theorem'

Fermat's Last Theorem, sometimes called Fermat's Conjecture, took over 300 years to prove.

Kepler left the world a puzzle that resisted all attempts at formal proof for 400 years: the Kepler Conjecture.

Kepler's Conjecture looks at how you can pack a bunch of equally sized spheres into the smallest possible space; he says there are two most efficient ways: cubic close packing and hexagonal close packing.

Kepler was right. A formal proof of his conjecture was published in 2015 by Thomas Hales and coworkers.

It turns out that Kepler's ideas about packing are useful in modern chemistry, where atoms in metals are arranged in close packed arrangements: for example copper's atoms are cubic close packed, while magnesium's atoms are hexagonal close packed.

Logarithms

In 1616 Kepler became aware of John Napier's invention of logarithms.

Using logarithms, any multiplication can be turned into an addition; any division can be turned into a subtraction.

For example, adding 3.5627685 to 3.7736402 by hand is much easier than multiplying 3654 times 5938. And in Kepler's day, everything had to be calculated by hand!

Napier's logarithms allowed mathematicians to greatly simplify their calculations. Kepler was overjoyed when he learned of them. And no wonder: he carried out a huge number of calculations in his work, and logarithms sped everything up enormously.

But Kepler went one step further.

Mathematicians had not been able to understand how logarithms worked. They just saw that they seemed to give the right answers.

Kepler saw that if logarithms actually had no firm mathematical basis, his calculations might be discredited someday.

He overcame this hurdle in the way any genius would - he himself proved how logarithms transform multiplications and divisions into additions and subtractions.

Kepler's proof allowed all mathematicians to use logarithms with no misgivings.

The End

In Kepler's time, Central Europe was convulsed with tensions between Catholicism and Protestantism - resulting in the Thirty Years' War.

Symbolic of the paranoia of these times, Kepler's nature loving, herbalist mother was arrested in Württemberg in 1620, charged with witchcraft. She was held in prison for over a year, and the tortures she faced if she did not confess to witchcraft were described to her in detail. Kepler himself traveled to Württemberg and successfully defended his mother, finally winning her release.

Kepler moved around a lot during the last few years of his life. His job as a mathematician disappeared and, in an effort to make ends meet, he ended up casting horoscopes for a military commander - General Wallenstein.

Johannes Kepler died after falling ill at the age of 58, on November 15, 1630 in the German city of Regensburg. He was survived by a son and a daughter from his first marriage, to Barbara Müller, who died rather young. He was also survived by his second wife, Susanna Reuttinger, and two sons and a daughter from that marriage.

Today Kepler's grave is lost. The graveyard he was buried in was destroyed during religious battles a few years after he was buried.

Although Kepler cast horoscopes, his feelings about what was important in his work are summed up in these words:

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Lived 1571 to 1630. Johannes Kepler played a key role in the profound changes in human thinking that took place during the the scientific revolution. In Kepler's lifetime: religion clashed with religion religion clashed with science the old ideas of Ptolomy and Aristotle clashed with the new discoveries of Copernicus

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Lived 1596 - 1650.
René Descartes invented analytical geometry and introduced skepticism as an essential part of the scientific method. He is regarded as one of the greatest philosophers in history.

His analytical geometry was a tremendous conceptual breakthrough, linking the previously separate fields of geometry and algebra. Descartes showed that he could solve previously unsolvable problems in geometry by converting them into simpler problems in algebra. He represented the horizontal direction as x and the vertical direction as y. This concept is now indispensable in mathematics and other sciences.

Beginnings

René Descartes was born into a well-educated, upper-class family on March 31, 1596 in the French village of La Haye en Touraine. The village is now called Descartes, Indre-et-Loire in his honor.

René's father was Joachim Descartes, a lawyer at Brittany's Court of Justice. His mother was Jeanne Brochard, daughter of the Lieutenant General of Poitiers. René was their third child.

A year after René's birth his mother and her fourth child died during childbirth.

René's father's worked six months of the year in the Court of Justice in Rennes, about 200 miles (300 km) from their home. René was raised by his grandmother and his great-uncle. His father remarried when René was four and began living in Rennes permanently. Despite this, there was always affection between René and his father.

From birth René suffered poor health and had a permanent cough. Local doctors thought he would not survive infancy. His father employed a nurse who devoted herself to René's care. As an adult he believed his nurse saved his life - he paid her a permanent pension.

Education

At the age of about ten or eleven René was finally considered healthy enough to begin school. He boarded at the Jesuit School at La Flèche in Anjou. In a concession to his delicate health he was allowed to rise later in the morning than other students.

René spent seven or eight years at La Flèche learning logic, theology, philosophy, Latin and Greek. In his final two years he also learned mathematics and physics. The physics was that of Aristotle - almost entirely wrong.

He was a boy of prodigious curiosity, asking questions endlessly.

René learned something of Galileo's work including his recent amazing discovery of Jupiter's moons. At this time, Galileo had still not published his greatest works overturning Aristotle's physics; his trouble with the Catholic Church lay in the future.

At the age of 18, in 1614, René Descartes left La Flèche. Later he recorded his thoughts about his education as follows:

On Mathematics

On Philosophy

On the Sciences

The Law, the Army, and Mathematics

His father encouraged René Descartes to follow in his footsteps and study law. He did this, graduating from the University of Poitiers in 1616, aged 20, with a diploma and license in church and civil law.

Rather than becoming a lawyer, however, Descartes went traveling for about two years, including spending some time in Paris. He joined the Dutch States Army in Breda in 1618 and began studying engineering in a military academy. He soon met the Dutch scientist and philosopher Isaac Beeckman. In 1619 Descartes wrote Beeckman:

Descartes, aged 23, was now profoundly serious in his desire to make new discoveries in mathematics.

René Descartes' Contributions to Science

The Miracle

On November 10, 1619 Descartes was dozing in a warm, stove-heated room in the German town of Neuburg an der Donau.

There he had a series of dreams that would ultimately change the way scientists work. He believed a spirit sent by God gave him new ideas about:

The Scientific Method

Analytical Geometry

Philosophy

18 years later, in 1637, he published his ideas in Discours de la mèthode (Discussion of the Method), La Gèomètrie (Geometry), Les Mètèores (Meteorology), and La Dioptrique (Optics). The first two of these works contain his most significant contributions.

The Method

In Discussion of the Method Descartes shared his framework for doing science.

One of his main lines of thought was skepticism - that everything should be doubted until it could be proved.

His four main ideas for scientific progress were:

1. Never accept anything as true until all reasons for doubt can be ruled out.

2. Divide problems into as many parts as possible and necessary to provide an adequate solution.

3. Thoughts should be ordered, starting with the simplest and easiest to know, ascending little by little, and, step by step, to more complex knowledge.

4. Make enumerations so complete, and reviews so general, that nothing is omitted.

It is ironic that Descartes' own method might lead us to doubt that a dream 18 years earlier could have been the true source of his ideas!

Analytical Geometry

Descartes made the revolutionary discovery that he could solve problems in geometry by converting them into problems in algebra.

In La Gèomètrie he showed that curves could be expressed in terms of x and y on a two-dimensional plane and hence as equations in algebra.

The Cartesian coordinate system used in the image below is named in his honor. (Descartes' name in Latin is Cartesius.)

Descartes never actually drew an x- or y-axis in his work. These were assumed in his diagrams. The axes were formally introduced by the mathematician Frans van Schooten and other mathematicians in Leiden who translated La Gèomètrie from French into Latin, while developing it further. Latin editions of La Gèomètrie were released in 1649, 1659 and 1661.

Descartes also introduced the modern notation for exponents. For example, rather than writing a.a.a he would write a ³.

By unleashing the mathematical power of algebra to tackle problems in geometry, Descartes surpassed the expertise of Ancient Greece's brilliant geometers: he could now solve problems that had defeated them.

Analytical geometry was independently invented earlier by Pierre de Fermat, who lived in France at the same time as Descartes. Fermat worked on mathematics for his own pleasure and often kept his results private. He did, however, enjoy issuing challenges to other mathematicians to solve problems.

In 1638 Fermat sent a work entitled Introduction to Plane and Solid Loci to the mathematician, Marin Mersenne, to show how problems he had posed at an earlier date could be solved. Fermat's approach was different from Descartes'. Descartes showed how geometry could be expressed as algebra; Fermat showed how algebra could be expressed as geometry.

Influencing Isaac Newton and the Invention of Calculus

Calculus has been crucial to the progress of mathematics and the sciences. It was developed in the 1660s by Isaac Newton, and developed independently in the 1670s by Gottfried Leibniz.

In La Gèomètrie, Descartes showed how he could find tangents to curves. This process is a vital part of differential calculus. His mathematical competitor Fermat was also able to find tangents to curves; his methods were actually simpler than Descartes'. Both Descartes and Fermat helped guide Newton and Leibniz's development of calculus.

Silenced by Fear of the Church

Four years before he released his 1637 works, Descartes had intended publishing The World.

In 1633, however, he learned that the Catholic Church had tried Galileo for heresy and sentenced him to life in prison. This was reduced to permanent house arrest because Galileo was rather elderly. The Church also prohibited Galileo's works.

Descartes, like Galileo, believed the sun sits at the center of the solar system. He decided not to risk the Church's wrath and did not publish The World. (Galileo could have been burned at the stake if his trial had gone worse than it did.)

Philosophy

Descartes is regarded as one of the greatest philosophers of all time. Here we are concerned with science rather than philosophy, so we will restrict ourselves to noting his most famous declaration:

"I think therefore I am."

This could also be expressed as:

"I can think, therefore I exist."

Descartes regarded this statement as the unshakeable foundation that all other philosophy could be built upon.

His most famous philosophical work is Meditations on First Philosophy, published in 1641.

Deducing the Laws of Nature from First Principles

Descartes' most comprehensive work, Principles of Philosophy, was published in 1644. In it he tried to deduce all of nature's laws from first principles. Although the book had much to commend it to philosophers, its science was incorrect.

He argued that action at a distance is impossible and agreed with the Ancient Greek philosopher Aristotle that there could be no vacuum. Soon, however, all his power as a philosopher would be defeated by scientific experiments.

An experiment is a question which science poses to Nature, and a measurement is the recording of Nature's answer.

Max Planck, Theoretical Physicist

In 1654 Otto von Guericke constructed the first vacuum pump. In 1662 Robert Boyle demonstrated that the magnetic force can travel through a vacuum, establishing that action at a distance is possible.

Unfortunately Descartes did not live long enough to learn of these developments.

Some Personal Details and the End

Descartes was wealthy enough to pursue his own interests. His father gifted him a number of properties which Descartes, at the age of 24, sold. This raised enough money for him to live on comfortably for the rest of his life.

Descartes spent much of his life on the move. He lived for 20 of his later years in various locations in Holland. He also studied and taught mathematics there. He found he could work better in Holland, with fewer distractions than in France.

Although he never married, in 1635, aged 39, he became a father. His partner was an Amsterdam servant, Helena Jans van der Strom. Their daughter was named Francine. Mother and daughter lived with Descartes in his house - he told people Francine was his niece. He planned to educate his daughter in France, but sadly, at the age of five, she died of scarlet fever. Francine's mother later got married, with Descartes playing a fatherly role by paying the wedding dowry.

In 1649 Descartes was invited to Stockholm by Queen Christina of Sweden. She wanted him to set up a new academy of science.

René Descartes died, aged 53, of pneumonia in Stockholm on February, 11 1650. He was buried at the Adolf Fredriks Church in Stockholm.

In death, as in life, Descartes was mobile. 16 years after his first burial his remains were moved and buried in the Saint-Ètienne-du-Mont church in Paris, France. In 1819 his remains minus skull and finger were moved again, this time to the Abbey of Saint-Germain-des-Près in Paris, where he now rests.

In 1663, despite his efforts to avoid such a fate - he regarded himself as a devout Catholic - a number of Descartes' works joined Galileo's on the index of books prohibited by the Catholic Church. Over 300 years later, in 1966, this index was finally discontinued.

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Further Reading
René Descartes
The Method Meditations and Philosophy
M. Walter Dunne, Washington and London, 1901

Elizabeth S. Haldane
Descartes: His Life and Times
John Murray, London, 1905

René Descarte, translators David E. Smith and Marcia L. Latham
The Geometry
Dover Publications Inc. 1954

Tom Sorell
Descartes (Past Masters)
Oxford University Press, 1987

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Lived 1596 - 1650. René Descartes invented analytical geometry and introduced skepticism as an essential part of the scientific method. He is regarded as one of the greatest philosophers in history. His analytical geometry was a tremendous conceptual breakthrough, linking the previously separate fields of geometry and algebra.

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Sir Isaac Newton was born especially tiny but grew into a massive intellect and still looms large, thanks to his findings on gravity, light, motion, mathematics, and more.

Subjects

Mathematics, Physics

Image

Isaac Newton Kneller Painting

Far more than just discovering the laws of gravity, Sir Isaac Newton was also responsible for working out many of the principles of visible light and the laws of motion, and contributing to calculus.

Photograph of Sir Godfrey Kneller painting by Science Source

Legend has it that Isaac Newton formulated gravitational theory in 1665 or 1666 after watching an apple fall and asking why the apple fell straight down, rather than sideways or even upward.

"He showed that the force that makes the apple fall and that holds us on the ground is the same as the force that keeps the moon and planets in their orbits," said Martin Rees, a former president of Britain's Royal Society, the United Kingdom's national academy of science, which was once headed by Newton himself.

"His theory of gravity wouldn't have got us global positioning satellites," said Jeremy Gray, a mathematical historian at the Milton Keynes, U.K.-based Open University. "But it was enough to develop space travel."

Isaac Newton, Underachiever?

Born two to three months prematurely on January 4, 1643, in a hamlet in Lincolnshire, England, Isaac Newton was a tiny baby who, according to his mother, could have fit inside a quart mug. A practical child, he enjoyed constructing models, including a tiny mill that actually ground flour-powered by a mouse running in a wheel.

Admitted to the University of Cambridge on 1661, Newton at first failed to shine as a student.

In 1665 the school temporarily closed because of a bubonic plague epidemic and Newton returned home to Lincolnshire for two years. It was then that the apple-falling brainstorm occurred, and he described his years on hiatus as "the prime of my age for invention."

Despite his apparent affinity for private study, Newton returned to Cambridge in 1667 and served as a mathematics professor and in other capacities until 1696.

Isaac Newton: More than Master of Gravity

Decoding gravity was only part of Newton's contribution to mathematics and science. His other major mathematical preoccupation was calculus, and along with German mathematician Gottfried Leibniz, Newton developed differentiation and integration-techniques that remain fundamental to mathematicians and scientists.

Meanwhile, his interest in optics led him to propose, correctly, that white light is actually the combination of light of all the colors of the rainbow. This, in turn, made plain the cause of chromatic aberration-inaccurate color reproduction-in the telescopes of the day.

To solve the problem, Newton designed a telescope that used mirrors rather than just glass lenses, which allowed the new apparatus to focus all the colors on a single point-resulting in a crisper, more accurate image. To this day, reflecting telescopes, including the Hubble Space Telescope, are mainstays of astronomy.

Following his apple insight, Newton developed the three laws of motion, which are, in his own words:

Newton's Law of Inertia: Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it.

Newton's Law of Acceleration: Force is equal to the change in momentum (mV) per change in time. For a constant mass, force equals mass times acceleration [expressed in the famous equation F = ma].

Newton's Law of Action and Reaction: For every action, there is an equal and opposite reaction.

Newton published his findings in 1687 in a book called Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) commonly known as the Principia.

"Newton's Principia made him famous-few people read it, and even fewer understood it, but everyone knew that it was a great work, rather like Einstein's Theory of Relativity over two hundred years later," writes mathematician Robert Wilson of the Open University in an article on a university website.

Isaac Newton's "Unattractive Personality"

Despite his wealth of discoveries, Isaac Newton wasn't well liked, particularly in old age, when he served as the head of Britain's Royal Mint, served in Parliament, and wrote on religion, among other things.

"As a personality, Newton was unattractive-solitary and reclusive when young, vain and vindictive in his later years, when he tyrannized the Royal Society and vigorously sabotaged his rivals," the Royal Society's Rees said.

Sir David Wallace, director of the Isaac Newton Institute for Mathematical Sciences in Cambridge, U.K., added, "He was a complex character, who also pursued alchemy"-the search for a method to turn base metals into gold-"and, as Master of the Mint, showed no clemency towards coiners [counterfeiters] sentenced to death."

In 1727, at 84, Sir Isaac Newton died in his sleep and was buried with pomp and ceremony in Westminster Abbey in London.

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Isaac Newton: Who He Was, Why Apples Are Falling

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Sir Isaac Newton was born especially tiny but grew into a massive intellect and still looms large, thanks to his findings on gravity, light, motion, mathematics, and more.

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Printing Press - Invented, Gutenberg, Significance | HISTORY

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The printing press, which allows for the mass production of printed matter, originated in China before Johannes Guten…

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Although gunpowder first emerged in ancient China as an alchemical health treatment, its application in warfare shattered the medieval world. In many ways, it was the quintessential substance of the rapidly approaching modern era, with cultural exchange, scientific experimentation, and mass warfare all bound up with its history. Here, we shall examine the development of the first guns, personal firearms that created altogether different conventions from the sword and the horse.

Gunpowder: Lifeblood of the First Guns

The critical ingredient for the rise of the first guns in the Renaissance era was gunpowder. Most people with an interest in Medieval history know that gunpowder was an invention from Medieval China - one of the "Four Great Inventions" that Chinese scholars perfected in the Imperial age. The other three were the compass, paper, and printmaking, which were all also key components of the technological revolution which characterized Renaissance Western Europe. It's important that we understand that the Renaissance period was a period of dialectical interface between the West and Middle Eastern and East Asian cultures, where a constellation of technologies, goods, and ideas were exchanged back and forth, shaping all of these societies and changing world history. Gunpowder was, therefore, the archetypical technology of its time.

Chemically, gunpowder is a mixture of sulfur, carbon, and potassium nitrate (usually known as niter or saltpeter). It is a low explosive, as distinct from a high explosive, that burns comparatively slowly by modern standards. But to medieval people, this must have been the very crux of alchemy itself - the creation of fire, smoke, and violent force from the application of a small flame to some inert powders.

Gunpowder was invented in China sometime in the mid-1st millennium CE, possibly as early as the late Eastern Han dynasty. It was likely discovered as a by-product of alchemical experimentation - Taoist texts from the era demonstrate a preoccupation with transmutation (changing the chemical properties of materials, e.g. "turning lead into gold"), and saltpeter was a frequent ingredient in these experiments.

The earliest cast-iron reference to gunpowder appears in 808 CE, in which the text Zhenyuan miaodao yaolüe (真元妙道要略) gives a recipe of six parts saltpeter, six parts sulfur and one part birthwort herb. Initially applied to courtly firework displays, this substance was known as "fire medicine" (" huoyao" 火藥), reflecting its association with Taoist medicinal experimentation. Before 1000 CE, this early gunpowder was applied militarily, used for slow-burning fire arrows. The refinement of the art of powder-making resulted in much more powerful explosives, which were soon applied militarily as explosives and rocket propellants.

The ancestor of the first guns appeared in the first half of the 12th century, with a weapon known as the "fire lance". This was a spear with a gunpowder charge in a bamboo tube attached near the end of the shaft. At first, these were merely powder charges that would shoot a plume of directed flame, but later they were also loaded with fragmentary debris like broken pottery and iron pellets. It was used as an impact weapon, like a single-use short-range flamethrower-shotgun. However, it often isn't considered a true firearm, as it did not use the explosion to drive the projectile along the tube - the debris was merely "blown" forward along with the fire.

The Chinese Hand Cannon

What we might seriously consider as the first guns were hand-cannons that appeared in China in the late 13th century. Chinese scholars have debated the historical literature extensively, interpreting surviving texts and depictions in various ways - but a safe date for the earliest true cannon is likely 1280 CE. Emerging from a milieu of experimental gunpowder weaponry like the fire lance, grenades, and bombards, the Chinese hand-cannon was a simple tube with bulbous base, made from cast bronze (and later iron), often around a 1-inch bore and with a characteristic bulbous ignition chamber at the base to withstand the expansion of the powder explosion. Sometimes it had a socketed wooden handle at the base to permit it to be carried, but just as often it did not.

The earliest example is the Heilongjiang hand cannon, discovered in 1970, and dated no later than 1288 CE. Contemporary historical records talk of "fire tubes" ( huotong, 火筒) being used by government troops in action against rebels in the region. The hand cannon had no firing mechanism beyond a touch-hole, a small hole that accessed the ignition chamber and permitted the lighting of the powder with a spill. While these hand cannons were doubtless devastating weaponry, they were much more costly and unwieldy than a fire lance, weighing 10 lbs (4 kgs) or more. Both weapons remained popular simultaneously in China throughout the Late Medieval era. These were without a doubt terrifying weapons, which, according to the 14th-century text Yuanshi, sowed " such confusion that the enemy soldiers attacked and killed each other".

The First Guns in the West

The first guns in Western Europe appeared in the second quarter of the 14th century, around 1330 CE. Various works from this period began to depict what we might think of as "cannons", such as the image above of a large bolt-throwing gun from Walter de Milemete's 1326 work De Nobilitatibus Sapientii Et Prudentiis Regum. Gunpowder had been known in Western Europe from the High Middle Ages, likely having been spread along the Silk Road and by Chinese engineers employed by the Mongols; they had penetrated into Eastern Europe in the 1270s CE - but serious development of the first guns did not begin until a short while after the emergence of hand cannons in China. There is very little evidence for an independent invention of gunpowder weaponry in Western Europe. Although a German scholar called "Berthold Schwarz" (Berthold the Black) was frequently credited with its invention from the 15th century until the Victorian period, modern scholarship regards his existence as wholly legendary.

By the third quarter of the 14th century, hand cannons were widespread in European armies. Accounts of the Battle of Crecy (1346 CE) contain some early mentions of gunpowder weaponry, including small-caliber hand cannons, larger cast-metal bombards, and even ribauldequins which could fire volleys of iron bolts. Archaeologists have even unearthed several iron balls of matching caliber from the battlefield. Despite initial suspicion and slow adoption, by the early 15th century the Islamic world had also embraced firearms, with the Ottoman janissaries becoming a feared group of crack troops armed with hand cannons and grenades.

The Gunpowder Age Dawns

As with all new weaponry, the first guns did not upend conventional military wisdom overnight: there was a period of tactical experimentation and technological refinement in order to achieve the potential of the technology. Hand cannons were far slower to load than a bow, and even a crossbow. They were temperamental and unusable in poor weather, and were frequently a danger to their users. Their effective range was a fraction of other missile weaponry. But their destructive power was evident from the first.

Up until this point, artillery was merely a scaled-up version of hand firearms (i.e. the bombard was merely a large hand cannon), it was at this point that artillery and firearms parted ways. Cannons would go on to transform Renaissance warfare, giving commanders the ability to puncture walls and destroy castles, even fundamentally changing the whole construction of defensive fortifications to combat their immense power. The first guns in Europe began to give way to more advanced forms of weaponry, which would have their own world-shattering impact. We shall examine a few of them below.

The Arquebus

The first major development of the hand cannon was the arquebus. The word arquebus comes from the Dutch haakbus, meaning "hook gun", referring to the hook on the underside of the weapon which was used to prop the weapon up on walls, or, in the open field, on a forked rest. It was one of the first guns to draw together all of the features that we commonly associate with the first guns of the Renaissance by the end of the 15th century. Gone was the hand cannon's bulbous firing chamber: improved metalwork meant that the smoothbore barrel could be straight.

It now had a priming pan, a secondary scoop on the exterior of the gun that was filled with powder in order to ignite the main charge within the barrel. It had a proper firing mechanism called a matchlock, the earliest form of trigger. This was a hinged arm fitted with a smoldering piece of tow rope - pulling the trigger would bring the end of the rope to the priming pan. It even had a simple wooden stock, likely inspired by contemporary crossbow design, permitting the gun to fire with far greater accuracy and mobility from the shoulder. These remained inaccurate and finicky, with many soldiers complaining that their slow matches would go out in the rain - but they were a vast improvement over cumbersome hand cannons.

The first force to employ the arquebus in large numbers was the Black Army of Hungary at the close of the 15th century, of whom one-in-four soldiers were arquebusiers. The legendary German-speaking mercenaries known as Landsknechts began to use mixed-unit tactics, with arquebusiers and longsword wielders mixed into pike squares. The adoption of large numbers of these first guns permitted the development in this era of firearm tactics, such as the volley fire, which was pioneered independently by Chinese and Ottoman generals.

An enormous step forward for the first guns came with the invention of the wheellock. Hitherto, all of these early firearms had been lit by some external source of ignition - either a taper dropped into a touch-hole, or a slow match clamped in a trigger mechanism. The wheellock, which appeared in the early 16th century, was the first gunpowder weapon to be self-igniting. It achieved this with an elaborate spring-loaded mechanism that would grind a toothed cog against a piece of pyrite to generate sparks - exactly like a modern cigarette lighter.

Once wound and loaded, a wheellock weapon could be fired with one hand quite easily, and barring complete mechanical failure there was very little chance they would go off accidentally. The major drawback was that they required enormous skill and cost to manufacture - and so they were mostly made as fowling pieces for wealthy patrons, although several examples we have were clearly made as early military pistols.

The First Guns and the Emergence of the Musket

The musket, which emerged in the middle of the 16th century as a heavier variant of the arquebus, ultimately spelled doom for the steel armor of the Late Middle Ages. With the innovation of the snaphance lock (a forerunner of the well-known flintlock that developed from the wheellock to strike its own sparks) muskets became portable, reasonably reliable, and simple to manufacture. Where even the arquebus was unwieldy and inaccurate, muskets could now be fielded as an independent force.

Experiments with replicas of early muskets have shown that they could puncture 4mm of steel. While there was a constant arms race between steel armor and the first guns throughout the Late Middle Ages, the musket was the trump card. It made contemporary forms of all-encompassing plate armor more or less irrelevant, and the armored knight of the Renaissance era was rapidly relegated to the tournament field.

Personal body armor did not disappear overnight, but it changed in form and became much thicker: there is evidence, particularly among cavalry armor, that demonstrates attempts to make bulletproof helms and breastplates. But many troops - particularly poorer soldiers - began to discard their increasingly cumbersome armor entirely, ushering in the post-armor age of Early Modern warfare, fought in uniform jackets and breeches rather than chainmail and plate.

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The First Guns: How Gunpowder Overcame the Sword

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The Renaissance era saw the rise of the first guns in Western Europe, and they changed the face of warfare forever. This is their story of fire and steel.

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Benchmark History 9-10 A) Explain connections between the ideas of the Enlightenment and changes in the relationships between citizens and their governments.

Teacher will need copies of attached primary sources and PowerPoint presentation, word search, and answer key.

Day 1- Brainstorming on what students know about Galileo will start the class.

PowerPoint introducing students to Galileo will be shared the first day, ending with questions that may arise.

Students may be divided into groups to study these sources, or all students study all documents.

Follow with a discussion with students, focused on the questions about the Scientific Method and the nature of Galileo's conflict with authorities in the Roman Catholic Church.

Assessment: Evaluation of word search ( word search key) and teacher assessment of discussion participation.

Catherine Means, Licking Heights High School, Newark, Ohio

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Benchmark History 9-10 A) Explain connections between the ideas of the Enlightenment and changes in the relationships between citizens and their governments. Teacher will need copies of attached primary sources and PowerPoint presentation, word search, and answer key. Day 1- Brainstorming on what students know about Galileo will start the class.

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https://www.mat.uc.pt/~helios/Mestre/Novemb00/H61iflan.htm

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The Strange History of the Invention of the Thermometer

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Having your temperature taken is a regular feature of life amid COVID-19. Here's the origin story of the tool that's had us all on edge.