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 Kepler… and 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 as “Tycho,”
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 was—wait for it—over 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 castles—until
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, and—most importantly—huge,
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
sometimes “stars” streaked around—these
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
Empire—where 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 of Tübingen.
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.
Kepler—who used to call himself a “mangy
dog” because he was so full of self-doubt—chose 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 models… and
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 vary—because the planet will
travel faster when it’s closer to the sun—you
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
speeds—and 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 the “music 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 math—all 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 them—science
is a team sport!)
But the most famous astronomer from this period
gave astronomers a true research paradigm—ways
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
“stars” orbiting Jupiter—which 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.
Soon after, Galileo went on to make precise
observations of Venus, Saturn, and even Neptune.
Neptune was ultra-dim through the lens of
his telescope, a mere thirty-times magnification
compared to the naked eye.
The best was yet to come.
In his Dialogue Concerning the Two Chief World
Systems of 1632, Galileo explained the new
astronomy of Copernicus to a wide audience.
And he did this in terms of a debate within
science about what counts as good evidence.
That is, Galileo saw the birth of a new scientific
paradigm as revolutionary!
Galileo argued publicly with geocentrists
and believers in Tycho’s hybrid model.
Galileo argued that the tides demonstrate
that the earth indeed moves, and that Copernicus’s
model is right.
Saying that, as the Earth moves, the oceans slosh around on its surface. He didn't get everything precisely right.
Interestingly, Galileo knew about Kepler’s
theories but didn’t seem interested in them.
Unfortunately for Galileo, the Church also
saw his work as revolutionary.
The Inquisition banned him from publishing
any new work.
But Galileo eventually found
a Dutch publisher for his magnum opus, Two
New Sciences.
Published in 1638, it would become one of
the foundational texts detailing a new scientific
method…
Next time—we’ll dive into Galileo’s
thoughts about how to do science and meet
two other key scientific methodists, Francis
Bacon—who was not also Shakespeare!—and René Descartes.
Crash Course History of Science is filmed in the Dr. Cheryl C. Kinney studio in Missoula, Montana
and it’s made possible with the help of all this nice people and our animation team is Thought Cafe.
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