National Geographic News
Painted portrait of Galileo Galilei by Ivan Petrovich Koler-Viliandi.

Galileo Galilei discovered that the Earth orbits the sun, an observation for which he was put under house arrest for the last eight years of his life.

Photograph by The Gallery Collection/Corbis

Dan Vergano

National Geographic

Published February 15, 2014

Not every astronomer can claim to have enjoyed both the attention of the Inquisition and the Indigo Girls, but then again, Galileo was no ordinary genius.

Discoverer of moons, toppler of Aristotle's physics, and celebrated loser of history's most famous heresy trial, Galileo Galilei's greatest invention, in truth, was our own modern world.

On the 450th anniversary of his birth today, February 15, 2014, it's worth taking a telescopic look at the achievements of this unparalleled genius of the Renaissance. Born in 1564 in Pisa, Italy, Galileo lived to the age of 77, a life span that saw the start of the scientific revolution in Europe. (See also: "Galileo's Telescope at 400.")

Galileo is still in the news. An optical illusion he discovered in the 1600s caused Venus to appear much larger and blurrier—a "radiant crown," as Galileo called it—when seen through a telescope than when viewed with the naked eye.

The puzzle was finally understood just this week. Neuroscientists from the State University of New York College of Optometry report that the answer lies in the wiring of our visual brain cells. The brain responds to light and dark objects differently, so the brightness of a planet distorts its apparent size when it is seen against the dark background of space.

Heaven and Hell

"Infinite thanks to God," Galileo wrote in 1610, "for being so kind as to make me alone the first observer of marvels kept hidden."

He was celebrating his discovery of Jupiter's four large moons: Io, Europa, Ganymede, and Callisto. Originally he wanted to name the moons after his noble patrons, four brothers of Florence's famed Medici family called Cosimo, Francesco, Carl, and Lorenzo. Other astronomers, perhaps thankfully, assigned more elevated names to the moons, ones taken from mythology for the consorts of Jupiter, king of the gods.

Those moons revealed that some objects revolved around something other than the Earth, which helped Galileo to discover heliocentrism, or the fact that the Earth circles the sun. This finding, in turn, would earn him the attention of the Inquisition, which investigated religious rebellion and heresy in the world of 16th-century Italy. The Vatican officially apologized in 2000 for Galileo's heresy trial, which resulted in the scientist being kept under house arrest for the last eight years of his life.

Photo of the four large Galilean moons of Jupiter.
Photograph by NASA/Roger Ressmeyer/CORBIS
Using telescopes he built, Galileo was the first to identify the four large moons of Jupiter.

Cannonball Physics

Galileo's most famous experiment, which he likely never really performed, was the 1589 dropping of cannonballs with different masses off the Leaning Tower of Pisa. The goal of this experiment was to show that objects fall at a uniform rate, that gravity doesn't make heavier objects fall faster.

That notion was contrary to classic Greek physics, which held that heavier objects fall faster. In 1971 the experiment was repeated on the moon (to remove the effects of air resistance) by Apollo 15 astronauts, who dropped a hammer and a feather to confirm Galileo's observation.

What was notable about the experiment was precisely that it was an experiment. Earlier models of scientific inquiry were reasoned entirely in the mind or argued from theological principles. Galileo, by contrast, advanced the fundamental idea that science relied on experiments to prove its contentions. This simple idea—prove it—was radical at the time.

Galileo went even further, pioneering the idea that mathematics are essential to scientific observations, and abjuring the literary hand-waving of ancient texts. He was the father of mathematical physics, reporting his observations in tables that inspired today's lab books. The diagrams he made depicting astronomical objects are clear forerunners to modern ones.

He put his knowledge to practical use, grinding the lenses for improved telescopes that allowed him to make astronomical discoveries ahead of other scholars—spotting moons, finding sunspots, and peering into the craters of Earth's moon.

As recounted in his volume Starry Messenger, Galileo crafted a telescope for the sailing masters of Venice that magnified views by at least eight times, helping them look out for pirates on trading voyages.

Illustration of Galileo Galilei dropping a cannonball and a wooden ball from the top of the Leaning Tower of Pisa.
Image by Hulton Archive/Getty
According to legend, Galileo dropped a cannonball and a wooden ball from the Leaning Tower of Pisa to see which fell faster.

Open Access Science

In his writings and books, some published in Holland to avoid the wrath of the Inquisition, Galileo gave shape to an ideal that exists in the scientific community to this very day: that scientists are united in their quest to understand the unknown and that their voyage of discovery transcends national borders. Galileo widely corresponded with other natural philosophers and the great innovative minds of his time, such as Johannes Kepler, who first wrote down the laws of orbital motion.

In writing down their discoveries, Galileo and his contemporaries created the beginnings of the system of scientific correspondence that we know today as scientific journals, where discoveries are openly described by their methods, results, and possible shortfalls.

This was quite a contrast to the gnomic writings of alchemists, who cloaked their recipes in mythological allusions and double-talk. The open discourse of the scientific enterprise is one of the abiding gifts of the Renaissance. (Although it is worth noting that Galileo resorted to scrambling news of his findings in code in letters to Kepler.)

Galileo not only wrote to fellow scholars, he also wrote for the public, notes historian Doug Linder in his account of the trial of Galileo. "He seemed compelled to act as a consultant in natural philosophy to all who would listen," Linder writes. "He wrote in tracts, pamphlets, letters, and dialogues—not in the turgid, polysyllabic manner of a university pedant, but simply and directly."

That talent for communication was quite likely what got him in hot water with religious authorities, ending with the heresy trial, one of history's crueler attacks on independent thinking. The trial haunted the Vatican for centuries; its treatment of Galileo added momentum to the Enlightenment's demand for intellectual freedom, which opened the way for such documents as the U.S. Constitution and the United Nations Universal Declaration of Human Rights.

The scientist's communication skills were said to be overbearing at times. "Everyone agrees that Galileo was an incorrigible egotist, so full of himself that he repeatedly misjudged his ability to persuade the authorities of his own opinions," astronomical historian Owen Gingerich of the Harvard-Smithsonian Center for Astrophysics noted in a recent review of Galileo biographies.

Whatever his flaws, "Galileo was the most articulate spokesman for the new astronomy, the pioneer who set observational astronomy on its modern track," Gingerich said.

And beyond his scientific achievements, Galileo is remembered in the popular imagination as a courageous truthseeker, a view expressed in the song "Galileo" by the folk rock group Indigo Girls. He was, they sing, "king of night vision, king of insight."

Remembered, too, 450 years after his birth, is Galileo's (likely apocryphal) rejoinder to the Inquisitors, "Yet still, it moves." He was talking about the Earth, which today everyone knows as one of many planets, a place happily shaped more by Galileo than by any of his persecutors.

Follow Dan Vergano on Twitter.

James Ph. Kotsybar
James Ph. Kotsybar


  --  James Ph. Kotsybar

If Galileo Galilei weren’t banned

by those who feared he challenged status quo,

whose doctrine wouldn’t let them understand

that truth is sought, not granted, we might know

another world as colonists by now.

If Rome had not felt threatened, but had faced

the Renaissance and let fact have its say,

if only his pronouncements were embraced

as tightly as the dogma of his day,

then trips to new stars might be underway.

If science had the freedom to enthrall,

and Inquisition challenged held beliefs

not “heretics” who’d taken up that call,

our planet might have many fewer griefs.

Pervaiz Malik
Pervaiz Malik

Viva Galileo!!! you are amazing even after passing of 450 years.

k.m. mathew
k.m. mathew

Can we tolerate such ordinary people? We will gain a lot than tolerating god men, god women.  East or west, north or south the maximum destruction by way of Apocalypse, kaliyuga etc.,  comes from dogmatic group beliefs not from free,ordinary and independent individual minds.  For whom we are polluting, for whom we are producing toxin filled farm products and for whom side effect laden medicines are manufactured? We know the answer.  But mute Miltons we are  and Galileo refused to be silent.   

Mitali Sinha Roy
Mitali Sinha Roy

The most glorious scientist of our world.I think,this is too much great thing that he is still ialive in our mind even after 450 years.Hats Off to you great scientist...

Mark Damiano
Mark Damiano

I love these gross oversimplifications of Galileo's conflict with the church.  In fact, Galileo was convicted for disobedience (what we today would call "contempt of court"), not for his scientific beliefs.  If Galileo had shown the same disobedience to any other sovereign authority of the same era (say, the king of England) he would have lost his head.  Instead, he died of natural causes in his own bed, in his own comfortable villa in Arcetri.  If you're looking for a genuine martyr for freedom of thought, try looking up Thomas More. 

Antonio  Nafarrate
Antonio Nafarrate

My heroes are Aristarcus, of Samos, Copernicus, Galileo, Newton (great scientist nasty man), A. Einstein (I share Horoscope with him but unfortunately I think very little of the horoscope makers) Well I like of these people because I studied Physics. In the last 20 years or so I became fan of a new hero and now on top of my list the shy, kind, suffering and the wonderful thinker Charles Darwin. I was looking at the skies since I was some 8 years old in the very dark unpolluted area of the Argentine Pampas. I came to the US as legal immigrant (now I am US citizen) I worked for IBM   San Jose Research for 5 years, later for 13 years with Xerox PARC, wanting to do practical work I joined Spectra Physics, the head of the Optics Division Dr. Gary deBell is still one of my very good friends. Later I went to Coherent were I worked in the Medical products such as CO2 lasers for medical surgery, Fiber optics for prostate cancer ablation, well you named I think I did it. While at Xerox I was granted a Social Service Leave to work with the Stanford Sleep Disorders Clinic to work with a patient that because of his blindness lived in a lunar rhythms day. I also was granted several US Patents. Thanks for your patience I get excited reviewing my past.  

Mandi Haberman
Mandi Haberman

Heroism at it's finest...probably my most idolized icon.

Cameron Spitzer
Cameron Spitzer

Copernicus rediscovered the heliocentric solar system.  Galileo discovered the church was teaching mistaken science and picked a fight with them about it.  If we should learn anything from Galileo's life, it's the wisdom of complete separation of church from state.

John Reeves
John Reeves

Does his insight enrich our world? or is it destroying it?  In some ways Fukushima, Bhopal, Overpopulation, CO2 pollution, Extinction, Acidification of the Oceans, etc. are all on Galileo also.  

Marek Undrul
Marek Undrul

"Those moons revealed that some objects revolved around something other than the Earth, which helped Galileo to discover heliocentrism, or the fact that the Earth circles the sun." 

Did someone forget about  Nicolaus Copernicus (1473–1543) and his 

De revolutionibus orbium coelestium printed in 1543, two decades before Galileo was even born?

Antoinette Hjelte
Antoinette Hjelte

Fantastic article.  From the Leaning Tower of Pisa, to the Moon.  Who knew?

Antoinette Hjelte
Antoinette Hjelte

Fantastic read, from the Leaning Tower of Pisa, to the Moon.  Who knew? 

Donn Christensen, Sr.
Donn Christensen, Sr.

It took the Vatican from the 16th century to the beginning of the 21st century to say they were wrong. Amazing that the rest of the world would recognize his genius so much sooner (centuries). But they depended on scientific fact, not the"Infallibility of the Faith"....

Camilo Bonilla O
Camilo Bonilla O

Discoverer of moons, toppler of Aristotle's physics, and celebrated loser of history's most famous heresy trial, Galileo Galilei's greatest invention, in truth, was our own modern world.

Eric Ringger
Eric Ringger

@Mark Damiano  Excellent context. However, Thomas More doesn't smell like such a rose, if you examine his persecution of William Tyndale.

Kevin Starnes
Kevin Starnes

@John Reeves  No, most of those sad and unfortunate events were a result of modern man's greed and ignorance. Galileo had neither of those traits. 

Following your flawed and obscured line of reasoning, I imagine that you'd blame Edison or Tesla for any accidental electrocutions. 

N. Ten
N. Ten

@Colorado Bob

That reflects abysmal  basic science in union dominated urban schools

N. Ten
N. Ten

@Christopher Johnson

Again, that reflects a dismal performance record in union dominated urban schools, as well as a problem with 29 million current US residents from Mexico who have no high school education.

Do look at the data on basic science scores. IN national testing on science , suburban kids average in 70th percentile. rural kids in 60th, home schooled kids 86th percentile, private school kids in the 90's and urban kids in the 20th and 30th

N. Ten
N. Ten

@Camilo Bonilla O

No. More like a rigid views of Aristotle. Aristotle was essentially the first scientist. He was rational. He made a few mistake sin astrophysics and biology, but it was the rigidity of later thinkers in western Europe caused the problem

The ancient Greeks invented the rational modern world. The problem in the intervening period was the destruction of rational thought due to the  reemergence of Torah though Christianity and Islam 

John Reeves
John Reeves

@Kevin Starnes @John Reeves

Only modern man exhibits greed and ignorance?  That seems a silly assertion.  According to the article, Galileo was a raving egotist, who didn't realize his own limitations.  Science often seems to be fools screwing around with powerful forces with no idea of the ramifications of what they are experimenting with.  Ramifications that as we enter the nuclear and genetic ages grow exponentially more dangerous.

Let's see I posed a question, which you seem to think is a line of reasoning.....  Good to see you using imagination and straw men instead of logic.   Galileo would be proud.

I do think it is an interesting question to consider.  Has science (which Galileo is considered the 'father' of) made us happier?  I honestly haven't decided and see points on both sides.

Obviously the idea of even considering this causes psychological pain to some.  Which to me seems a good reason to fully examine the question.  Others may of course disagree.


@John Reeves @Kevin Starnes
"I do think it is an interesting question to consider.  Has science (which Galileo is considered the 'father' of) made us happier?  I honestly haven't decided and see points on both sides."

Think about the real possibility of a solar flare knocking out electricity world over for 10 years, and then answer your own question. We would literally be back to kerosine lamps. No, thank you!


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