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  • Heliocentrism was central to revolution in European astronomy.

  • We'll follow this idea to its conclusion with Galileo.

  • But before we get there, there are two critical links between Copernicus and Galileo.

  • This is the story of Tycho Brahe and Johannes Keplerand a violent

  • math duel.

  • [INTRO MUSIC PLAYS]

  • There are a lot of quirky characters in the

  • history of science.

  • But Tycho Brahe is a true champion of quirk.

  • Traditionally referred to asTycho,” not by his last name, he was a Danish aristocrat,

  • born in 1546—three years after De rev dropped and Copernicus also dropped.

  • Tycho was a good astronomer.

  • But maybe a little too serious about knowledge: my dude got his nose cut off in 1566 during

  • a sword duel with his cousin and fellow rich person Manderup Parsberg.

  • Their beef waswait for itover mathematics.

  • You have to really love math to lose your proboscis over it.

  • After the duel, Tycho had prosthetic noses made that he could attach to his face with

  • wax.

  • But whenever he got angry, he'd heat up and start sweating, and the wax would melt

  • and his nose would fall off.

  • ...that's real.

  • In addition to an astronomer, Tycho was an alchemist and astrologer.

  • He became so well known as a scientist that the Danish king kept trying to give him castles

  • so he wouldn't move away.

  • And Tycho kept turning down castlesuntil he got his own private research island, Hven

  • On Hven, Tycho built two structures, Uraniborg, or the Castle

  • of the Heavens, and Stjerneborg, or the Castle of the Stars.

  • Together, these castles represented the most state-of-the-art research labs of the day.

  • Here, Tycho built a scientific empire.

  • He had his own printing press, paper mill, alchemical equipment, andmost importantlyhuge,

  • expensive instruments and an army of staff scientists working for him.

  • In fact, Tycho worked with his younger sister, Sophie.

  • Tycho and his staff produced some of the most precise naked-eye observations of the night

  • sky ever.

  • These were roughly twice as precise as similar observations by ancient Egyptian, Babylonian,

  • and Greek astronomers.

  • Tycho's observations were not surpassed by those made with telescopes for a hundred years.

  • Tycho believed in a geo-heliocentric cosmos.

  • In this model, the sun orbits the earth, but the other planets revolve around the sun.

  • So Tycho was moving away from Aristotle and Ptolemy.

  • And his hybrid model actually solved a bunch of the math problems astronomers were having

  • with the Ptolemaic model

  • But it also placed the sun on a collision course with the planets.

  • So, not perfect.

  • Even if the Tychonic model of the solar system had flaws, his observations paid off in other ways.

  • Tycho observed and took precise measurements of the same sky all the time, noting that

  • sometimesstarsstreaked aroundthese were comets.

  • In 1572, he saw a nova stella, er, a new star, which we now call a supernova.

  • He noted that this new star didn't have a tail or show any stellar parallax, meaning

  • an apparent shift in position against a background of distant objects.

  • This meant that the new star had to be really, really, incredibly far away—a true star

  • and not a comet.

  • Moreover, the appearance of a new star meant that the heavens could change!

  • God could straight up add new stars!

  • If you really believed your whole life that the heavens were perfect and unchanging, how

  • hard would it be to adjust those beliefs just because you saw one new dim little pinpoint

  • of light at night, a dot that nobody else cared about?

  • That's just what Tycho did: one year after the supernova, in 1573, he dropped his own

  • book: De nova stella, or On the New Star.

  • But after all that hard work, Tycho's life ended sadly.

  • The old Danish king died, and his nineteen-year-old son took over.

  • This not-super intellectual new king wanted his nobles to spend their energy on war, not science.

  • So he roused up opposition to Tycho's science castles, whipping up a mob to drive the patient

  • observer into exile.

  • Thus Tycho moved to Prague, in the Holy Roman Empirewhere he died after only two years

  • in exile, leaving behind an enormous meticulously detailed catalogue of observable stars and

  • one very well-trained assistant

  • Johannes Kepler was born in 1571 near Stuttgart, Germany.

  • His grandfather was rich, but his dad hadn't done so well, dying as a mercenary in the

  • Netherlands.

  • Little Joey went to school on scholarship at a Latin school, seminary, and then the

  • University ofbingen.

  • Which is still a great school today!

  • Go, uh, 'Bingers!?

  • After college, Kepler taught math.

  • Then, in 1600, Kepler so impressed Tycho that the older astronomer shared his secret data

  • sets with him, and the two become close collaborators.

  • Then politics happened: Kepler, a devout Lutheran, was told to convert to Catholicism or leave

  • Prague.

  • Keplerwho used to call himself a “mangy dogbecause he was so full of self-doubtchose exile.

  • When Tycho died in 1601, however, Kepler was immediately ordered to serve as the official

  • imperial mathematician and continue Tycho's work.

  • Politics!

  • Make up your mind!

  • As imperial numbers person, Kepler mostly provided the emperor with advice about astrology.

  • Remember that astronomy was seen as the less useful, theoretical cousin of the practical

  • art of astrology.

  • But Kepler, thank goodness, kept making time for astronomy.

  • In addition to the observing and cataloguing that he'd done with Tycho, Kepler worked

  • on optical physics.

  • And he observed a new supernova in 1604, in the foot of a constellation that is supposed

  • to depict a Greek dude fighting a giant snake!

  • (Or just holding it.

  • We aren't sure.)

  • Kepler wrote his own De nova stella around 1605.

  • But Kepler is famous thanks to the laws governing how planets move.

  • Kepler published Astronomia nova, or A New Astronomy, in 1609.

  • This mind-zapper of a tome came from a decade of looking at Mars to figure out mathematical

  • formulas that could predict its movements.

  • ThoughtBubble, show us the Red Planet.

  • Kepler calculated many versions of Mars's orbit using an equant point: this was an imaginary

  • point in space that Copernicus had already figured out how to get rid of.

  • Using an equant, Kepler made a model of Mars's motion that almost fit Tycho's crazy-meticulous

  • data set of years of observations.

  • Almost.

  • Kepler didn't just want a close model; he wanted to understand what was happening up there.

  • So he threw out his earlier modelsand tried an elliptical or ovoid orbit with the

  • sun in the center.

  • And, in writing up his Mars study, he proposed the first two laws of planetary motion.

  • The first law states that every planet has an elliptical orbit, with the sun at one of

  • the two foci of the ellipse, not its center.

  • The second law explains that, even though the speed at which a planet revolves around

  • the sun will varybecause the planet will travel faster when it's closer to the sunyou

  • can still figure out a constant speed for the planet, called an area speed.

  • This is the area described by the little pizza slice shape made when you draw a line from

  • the planet to the sun at time 1 and then again at time 2, whatever those times are, and then

  • fill in the area between the lines.

  • If you do this again later in the planet's trip, with the same interval between time

  • points, you'll get a slice with the same area.

  • Sounds complicated, but it was important for showing that planets do actually move at non-uniform

  • speedsand yet we can describe these motions very precisely using the right mix of math

  • and patient observation of the night sky!

  • Thanks Thoughtbubble!

  • Kepler didn't write the third law until 1619, by the way.

  • It explains the relationship between the distance from planets to the Sun and their orbital

  • periods.

  • This law was Kepler's attempt to explain the harmony of themusic of the spheres!”

  • Alright, so that might not make the best scene in an action movie: Kepler stops using an

  • imaginary dot to make circles move like eggs, and instead just draws a dang egg.

  • But this represented a clear break with Aristotle and Ptolemy and a millennium of Christian

  • thought.

  • And Kepler, unlike Copernicus, didn't hold back his theory for fear of ridicule by his

  • peers or condemnation by the Church.

  • In fact, religious ideas helped Kepler move toward a heliocentric, eccentric model: he

  • saw the sun as a symbol of God the Father, at the center of things, moving planets faster

  • when they came closer.

  • So when Kepler plugged the Mars data into his new model, and the numbers worked out,

  • he probably didn't rejoice at the triumph of secular thought over faith.

  • He rejoiced at a harmony of ideas: his faith, empirical data, and elegant mathall in

  • sync!

  • Kepler gave European astronomers a theory, backed by superb math, that explained natural

  • phenomena better than Aristotle, Ptolemy, Oresme, Copernicus, and Tycho could.

  • (Although Kepler built on work by all of themscience is a team sport!)

  • But the most famous astronomer from this period gave astronomers a true research paradigmways

  • to do science all day.

  • You might know Galileo Galilei, born in 1564, as the person

  • who dropped stuff off the side of a messed-up tower in Pisa.

  • If you recall episode one, though, you know that Galileo probably didn't conduct this

  • experiment: the first published account of it dates from 1657, fifteen years after Galileo died.

  • And Galileo worked on this theory a decade after he left Pisa.

  • That said, he did prove the uniform rate of falling bodies.

  • And Galileo did lots of other amazing things for science, earning him uncontested rockstar

  • status.

  • We'll learn more about his overall contributions next week.

  • Right now, let's talk star-gazing.

  • First, Galileo got his hands on a telescope in 1609 and refined this technology for years,

  • which led to more and better observations of distant planets.

  • In 1610, he dropped Sidereus Nuncius or

  • The Starry Messenger - what a very good title for this book - which was his telescope-enabled description of the earth's moon and the

  • starsorbiting Jupiterwhich were its moons.

  • His descriptions were based on literally never-before-possible observations and included accurate illustrations

  • showing mountains on our moon.

  • And these were good drawings, because Galileo had been trained as a professional artist!

  • And, according to Aristotle's cosmology, a planet could not orbit another planet other

  • than earth.

  • So Sidereus Nuncius represented an empirically based break with the older model.