Few people in history can claim as large a contribution to how we conduct and think about science as Galileo. His work revolutionized our entire outlook on what it means to study nature (and got him in some very hot water with the Roman Inquisition). He is perhaps best known for his championing of Copernicus’ heliocentric model (the one that says the Earth and other planets orbit the Sun), but that is by no means the full extent of his legacy. Far, far from it.

Galileo earned himself a place among the stars as Europe’s global navigation satellite system bears his name, and today we’re going to see how we did it.

A short review of his legacy

Galileo is certainly among the titans of science — in many ways, he’s one of its ‘founders’. His legacy includes contributions to the fields of physics, astronomy, math, engineering, and the application of the scientific method. Much of his work may seem mundane, basic scientific fact today, but in their time they were quite groundbreaking.

I spent quite some time considering what I would list as being his greatest single achievement. There’s no shortage of options; Galileo put in a lot of time and effort to study and describe physical properties, most notably those related to motion. He was an accomplished mathematician and inventor, designing (among others) several military compasses and the thermoscope. He was also the one to pick up the torch of modern astronomy from Copernicus, cementing the foundations of this field of study by proving his theories right. In his later years, under house arrest, he furthered kinematics and materials sciences.

Still, I wouldn’t list any of these as his crowning achievement. I would consider these to be evidence of Galileo’s curiosity, and his willingness to watch, measure, and consider before forming a belief, despite the weight of centuries-old religious institutions bearing down on him. He showed by personal example that nature can be understood through observation. In an age where not believing in Heaven hard enough could get you burned at the stake, Galileo was peering into its secrets using a weird brass tube and writing them down in numbers.

Showing others what science can do, and how one should go about it, is Galileo’s most important achievement. Its effects still ripple through the lives of every researcher to this day. He can be credited (or blamed) for us using complex equations instead of fancy philosophical speak in science today, as engineering students everywhere will no doubt be thrilled to know.

A short review of his life

Galileo (born Galileo di Vincenzo Bonaiuti de’ Galilei in 1564’s Pisa, Italy) was the son of lute-player and composer Vincenzo, and Giulia, a mother from “a prosperous family”. He learned to play the lute and the principles of music theory from his father, and in his young days toyed with the idea of becoming a priest. However, more practical matters (such as making it rain) weighed more heavily on his father’s mind, so he convinced Galileo to enroll for a medical degree at the University of Pisa in 1580.

He attended courses there for at least a year, and during this time he would have a chance encounter that would impact all of humanity — Galileo saw a swinging chandelier. He saw that no matter how much it would tilt one way or another, the chandelier would always take the same time to swing back around. Although he tried to keep away from mathematics up to this point (physicians were better paid than mathematicians), he was enraptured with the chandelier’s motion. When visiting home, he set up a pair of pendulums to study their properties. One geometry lesson later (which he attended “accidentally”) and Galileo was asking his father to let him study mathematics and natural philosophy instead — which Vincenzo agreed to.

Galileo spent the next 10 or so years studying math, physics, and fine art. He got a position as an instructor in the Florence Academy of Drawing Arts (Accademia delle Arti del Disegno) in 1588, and as the chair of mathematics at the university in Pisa in 1589. In 1592 he moved to Padua and started teaching geometry, mechanics, and astronomy, and until 1610 would conduct much of his theoretical and applied science work. Around 1615, his advocacy of the heliocentric model got him into trouble with the Catholic Church (and some of his fellow astronomers). The Inquisition would finally hold him on trial for (and find him guilty of) heresy in 1633. One of his works was banned and he was sentenced to “formal imprisonment at the pleasure of the Inquisition”, although this was adjusted to house arrest the following day. Legend has it that it was during this trial that Galileo uttered the famous phrase “and yet it moves“. Galileo spent the rest of his days in his home, refining his theories and thoughts and writing them down for posterity. He would die in 1642 after experiencing a fever, at the age of 77.

One fun fact about this trial is that Galileo’s name is heavily tied to the region of Galilee, northern Israel, which is an important place in Christian traditions. Although he styled his name in various ways (as was customary at the time), “Galileo” basically means “of Galilee”. So his full name, then, would be “Galileean of Galilee”. In his trial, a priest named Tommaso Caccini made sure to quote a Bible passage (acts 1:11) to the effect of “men of Galilee, why stand ye gazing up into heaven?” — which is a pretty sweet pun, all things considered.

Here’s a review of his inventions and breakthroughs.

Understanding how things fall

People have been studying how things move — which we now know as ‘kinematics’ — since times immemorial. After all, knowing how a particular spear or stone would behave after you throw it is a key skill in the savannah. But Galileo set its groundwork as a field of academic study.

Since the days of Aristotle, scholars in Europe believed that heavier objects fall faster than lighter ones. Galileo showed that this wasn’t the case, using balls of the same materials but different weights and sizes. In one of his infamous experiments, he dropped two such balls from the top of the leaning tower of Pisa to show that objects of different weights accelerate just as fast towards the ground (air resistance notwithstanding). There is quite a debate regarding this experiment — most historians seem to agree that it was more of a thought experiment, and wasn’t actually carried out. The truth is Galileo’s experiments in this area used a more reliable but less flashy bunch of inclined planes that he rolled balls down on.

In another experiment, he showed that objects follow a parabolic (ballistic) trajectory when travelling through the air. Here he used an inked bronze ball and an inclined plane with a piece that would send the ball on a horizontal plane at the bottom. The ball would accelerate towards the ground, exit the device on a horizontal path, then fall to the floor, leaving a small indent and a patch of ink. Galileo used these marks to measure the endpoints of the ball’s trajectory through space.

Galileo himself posited that in the absence of meaningful resistance of a medium, a falling body would fall with a uniform acceleration. He also wrote that objects in motion tend to retain their velocity, which we today know as Newton’s First Law of Motion.

“Imagine any particle projected along a horizontal plane without friction; then we know, from what has been more fully explained in the preceding pages, that this particle will move along this same plane with a motion which is uniform and perpetual, provided the plane has no limits.”

Galileo Galilei, Dialogues Concerning Two New Sciences.

His interest regarding motion and the falling of objects were tightly linked to Galileo’s interest in planets, stars, and the solar system. He would routinely regard the motion of planets as that of objects constantly falling in relation to one another in a frictionless environment — surprisingly on point for a guy in the 16th century.

Pendulums

Galileo’s work directly led to the creation of the first accurate clocks (by Christiaan Huygens in 1656). The duration of a pendulum’s swing is independent of its amplitude. Two pendula with different masses but the same length will have the same swing, and a pendulum with a longer arm will take longer to swing than one with a shorter arm — meaning that they can be used to accurately measure time. Galileo first made this observation and described the pendulum’s swinging motion using (if his pupil Vincenzo Viviani is to be believed) his own pulse as a means of keeping the time.

In the final days of his life, completely blind, Galileo would try alongside Viviani (who wrote his first biography) to create a pendulum clock. Unfortunately, his clock wasn’t very good. It was an improvement on the water clocks of old, but it also lost or gained time and, worst of all, would do so unpredictably. Galileo could never really use it in his astronomical studies due to how imprecise the clock was.

“One day in 1641, while I was living with him at his villa in Arcetri, I remember that the idea occurred to him that the pendulum could be adapted to clocks with weights or springs, serving in place of the usual tempo, he hoping that the very even and natural motions of the pendulum would correct all the defects in the art of clocks,” Viviani recounts.

“But because his being deprived of sight prevented his making drawings and models to the desired effect, and his son Vincenzio coming one day from Florence to Arcetri, Galileo told him his idea and several discussions followed. Finally they decided on the scheme shown in the accompanying drawing, to be put in practice to learn the fact of those difficulties in machines which are usually not foreseen in simple theorizing.”

Galileo’s experiments with bronze balls and inclined planes experiments revealed that all objects boasted the same falling acceleration independent of their mass, overturning the accepted (and wrong) consensus set since Aristotle and the ancient Greeks. He also demonstrated that objects thrown in the air travel along a parabola.

In the field of engineering

Apart from his theoretical pursuits, Galileo was also an accomplished engineer — meaning he could also turn his knowledge to the solving of practical problems. Most of these, historical accounts tell us, were attempts by Galileo to earn a little bit of extra cash in order to support his extended family after his father passed away.

Among his creations are a set of military compasses (sectors) that were simple enough for artillery crews and surveyors to use. Together with instrument maker Marc’Antonio Mazzoleni, he would produce 100 such compasses with an instruction manual for each. Galileo also offered training courses on how to use them that he himself would teach, for roughly twice the cost of one such instrument. He also created the thermoscope and thermometer — the latter of which used the thermal expansion of air to push water up in an attached tube.

He was also an early builder and user of telescopes and microscopes. Galileo, among a few select others, was the first to ever use a refracting telescope as an instrument to observe heavenly bodies, in 1609. During the same years, he also applied a telescope to magnify insect samples, and by 1624 he had used a compound microscope. The illustrations of them he published are our first concrete evidence of the use of such a device.

In fact, the term “telescope” was coined for Galileo’s device in 1611, as was the word “microscope”, both coming from members of the Accademia dei Lincei, where Galileo was made a member with much fanfare in 1611.

He was also consulted on engineering works on several occasions, most of them involving efforts to control river flooding or for the cutting of a channel for the Bisenzio River. 

On towards the stars

Here is perhaps Galileo’s most well-known field of work. He put in a great deal of effort developing the tools and processes needed to study the heavens — then used them, intensely.

In 1604, he observed Kepler’s Supernova, and concluded that it must be a distant group of stars. Like many of his other pursuits, this disproved Aristotle’s theory of the immutability of the heavens.

In 1609, he used the refractory telescope to look at the surface of the Moon and explain to those around him (presumably, much to their confusion and general worry about Galileo’s health of mind) that it was not, in fact, smooth. In the same year, he also looked at the four largest moons of Jupiter. He was, to the best of our knowledge, the first person to ever make either of these observations.

In 1610 he observed all the phases of the transition of Venus, which he offered as proof for the earlier but much disputed model of heliocentrism (with the Sun, ‘helios’, in the middle of the solar system). He also saw Saturn in the same year, although he believed its rings to be two other planets. In 1612, he spotted Neptune and described its motion, although he didn’t identify it as being a planet. Finally, Galileo noted and studied sunspots, various stars (and developed ways to measure their apparent size even without a telescope), and the Milky Way at large. Along the way, he also showed the Doge of Venice how to use the telescope.

His fascination with celestial bodies and defense of the heliocentric model is what eventually led to the Inquisition cracking down on him and his works. Galileo’s work was considered wholly incompatible with religious dogma, and much of it was banned or censored by the Inquisition following his trial.

But Galileo refused to be prevented from doing his work even after being found guilty of heresy. In the true spirit of the scientist, he would quip that he does 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” and that “wine is sunlight, held together by water” at one point in his life — a true researcher indeed, and an intensely likable guy.