Galileo Matters More Than Ever on His 450th Birthday

The scientist's insights continue to enrich our world.

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.

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.

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.

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.

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