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Italian astronomer Galileo Galilei provided a number of scientific insights that laid the foundation for future scientists. His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time - that all things revolved around the Earth.

[See also our overview of Famous Astronomers and great scientists from many fields who have contributed to the rich history of discoveries in astronomy.]

Galileo's experiments

The Ancient Greek philosopher, Aristotle, taught that heavier objects fall faster than lighter ones, a belief still held in Galileo's lifetime. But Galileo wasn't convinced. Experimenting with balls of different sizes and weights, he rolled them down ramps with various inclinations. His experiments revealed that all of the balls boasted the same acceleration independent of their mass. He also demonstrated that objects thrown in the air travel along a parabola.

At the same time, Galileo worked with pendulums. In his life, accurate timekeeping was virtually nonexistent. Galileo observed, however, that the steady motion of a pendulum could improve this. In 1602, he determined that the time it takes a pendulum to swing back and forth does not depend on the arc of the swing. Near the end of his lifetime, Galileo designed the first pendulum clock.

Galileo's telescope

Galileo is often incorrectly credited with the creation of a telescope. ( Hans Lippershey applied for the first patent in 1608, but others may have beaten him to the actual invention.) Instead, he significantly improved upon them. In 1609, he first learned of the existence of the spyglass, which excited him. He began to experiment with telescope-making, going so far as to grind and polish his own lenses. His telescope allowed him to see with a magnification of eight or nine times. In comparison, spyglasses of the day only provided a magnification of three.

It wasn't long before Galileo turned his telescope to the heavens. He was the first to see craters on the moon, he discovered sunspots, and he tracked the phases of Venus. The rings of Saturn puzzled him, appearing as lobes and vanishing when they were edge-on - but he saw them, which was more than can be said of his contemporaries.

Of all of his telescope discoveries, he is perhaps most known for his discovery of the four most massive moons of Jupiter, now known as the Galilean moons: Io, Ganymede, Europa and Callisto. When NASA sent a mission to Jupiter in the 1990s, it was called Galileo in honor of the famed astronomer.

In his book " Sidereus Nuncius" ("Starry Messenger"), published in 1610, Galileo wrote:

"On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavens through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, namely that three little stars, small but very bright, were near the planet; and although I believed them to belong to a number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude . . . When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night."

"I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury around the Sun; which was at length established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter."

Galileo may also have made the first recorded studies of the planet Neptune, though he didn't recognize it as a planet. While observing Jupiter's moons in 1612 and 1613, he recorded a nearby star whose position is not found in any modern catalogues.

"It has been known for several decades that this unknown star was actually the planet Neptune," University of Melbourne physicist David Jamieson told Space.com. "Computer simulations show the precision of his observations revealing that Neptune would have looked just like a faint star almost exactly where Galileo observed it."

Copernican system

In Galileo's lifetime, all celestial bodies were thought to orbit the Earth. Supported by the Catholic Church, teaching opposite of this system was declared heresy in 1615.

Galileo, however, did not agree. His research - including his observations of the phases of Venus and the fact that Jupiter boasted moons that didn't orbit Earth - supported the Copernican system, which (correctly) stated that the Earth and other planets circle the sun.

In 1616, he was summoned to Rome and warned not to teach or write about this controversial theory. But in 1632, believing that he could write on the subject if he treated it as a mathematical proposition, he published work on the Copernican system. He was found guilty of heresy, and was placed under house arrest for the remaining nine years of his life.

Galileo quotes

"And yet it moves."

"I have never met a man so ignorant that I couldn't learn something from him."

"I do 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."

"You cannot teach a man anything, you can only help him find it within himself."

"It is a beautiful and delightful sight to behold the body of the Moon."

"Wine is sunlight, held together by water."

- Find other quotes at GoodReads.com.
Additional resources

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Galileo Galilei: Biography, Inventions & Other Facts

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Italian astronomer Galileo Galilei provided a number of scientific insights that laid the foundation for future scientists. His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time - that all things revolved around the Earth.

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The science of astronomy took a huge leap forward in the first decade of the 1600s with the invention of the optical telescope and its use to study the night sky. Galileo Galilei did not invent the telescope but was the first to use it systematically to observe celestial objects and record his discoveries. His book, Sidereus nuncius or The Starry Messenger was first published in 1610 and made him famous. In it he reported on his observations of the Moon, Jupiter and the Milky Way. These and subsequent observations and his interpretations of them eventually led to the demise of the geocentric Ptolemaic model of the universe and the adoption of a heliocentric model as proposed in 1543 by Copernicus.

Galileo's Telescopes

The basic tool that Galileo used was a crude refracting telescope. His initial version only magnified 8x but was soon refined to the 20x magnification he used for his observations for Sidereus nuncius. It had a convex objective lens and a concave eyepiece in a long tube. The main problem with his telescopes was their very narrow field of view, typically about half the width of the Moon.

Galileo's Observations

Galileo made several key discoveries through his systematic use and refinement of the telescope.

The Moon

According to Aristotelian principles the Moon was above the sub-lunary sphere and in the heavens, hence should be perfect. He found the "surface of the moon to be not smooth, even and perfectly spherical,...,but on the contrary, to be uneven, rough, and crowded with depressions and bulges. And it is like the face of the earth itself, which is marked here and there with chains of mountains and depths of valleys." He calculated the heights of the mountains by measuring the lengths of their shadows and applying geometry.

Moons of Jupiter

Observations of the planet Jupiter over successive night revealed four star-like objects in a line with it. The objects moved from night to night, sometimes disappearing behind or in front of the planet. Galileo correctly inferred that these objects were moons of Jupiter and orbited it just as our Moon orbits Earth. For the first time, objects had been observed orbiting another planet, thus weakening the hold of the Ptolemaic model. Today these four moons are known as the Galilean satellites; Io, Europa, Ganymede and Callisto.

The Phases of Venus

Venus was observed to go through a sequence of phases similar to the Moon. This could not be explained in the Ptolemaic model but could be accounted for by either the Sun-centered Copernican model or the Earth-centered Tychonic model that had the other planets orbiting the Sun as it orbited the Earth. Galileo rejected Tycho's model as an unnecessary hybrid and used the discovery to consolidate his support of the Copernican model.

Sunspots

Along with contemporaries such as Thomas Harriot, David Frabicius and Christoph Scheiner, Galileo observed dark regions that appeared to move across the surface of the Sun. Debate centered on whether these were satellites of the Sun or actual spots on its surface. Galileo, in his Letters on Sunspots supported the sunspot interpretation and used it to show that the Sun was rotating. Its blemishes and imperfections again undermined the Aristotelian ideal of a perfect cosmos.

"Appendages" on Saturn

Galileo noted two appendages from the sides of Saturn. These disappeared then later reappeared. It was not until 1656 that the Dutch scientist, Christiaan Huygens correctly described them as rings.

Stars in the Milky Way

Even through a telescope the stars still appeared as points of light. Galileo suggested that this was due to their immense distance from Earth. This then eased the problem posed by the failure of astronomers to detect stellar parallax that was a consequence of Copernicus' model. On turning his telescope to the band of the Milky Way Galileo saw it resolved into thousands of hitherto unseen stars. This posed the question as to why there were invisible objects in the night sky?

Further Information

1. An excellent online source for all things related to Galileo is: The Galileo Project. It is hosted by Rice University and includes his writings, details on his experiments and observations and links. It is also the source for the image of Galileo at the top of this page.

2. Another worthwhile site is The Art of Renaissance Science: Galileo and Perspective. It has a wealth of diagrams matched with clear. concise text. There are some animations of his experiments.

3. The Institute and Museum of the History of Science in Florence has a wealth of detail on the history of astronomy including Galileo's work. Their new website is worth exploring. Much of it is in English although some sections, including an excellent simulation of early telescopes, is only available in Italian at present. They also have an excellent new site: Galileo's Telescope, the Instrument that Changed the World.

4. Afocal CCD Images Through a Galilean Telescope is an excellent resource that provides CCD images that approximate what the human eye would see through a Galilean telescope. It has images of the Sun, Moon, Venus, stars and nebulae. The site provides historical background and technical details.

5. Galileo's Sidereus nuncius or The Sidereal messenger is available in translation by A. van Helden from University of Chicago Press, 1989.

6. The Cambridge Illustrated History of Astronomy, ed Michael Hoskin, Cambridge University Press, 1997 provides a wealth of information and diagrams and is an authoritative yet readable guide to the topic.

7. The Sleepwalkers by Arthur Koestler is a classic book dealing with the development of astronomical thought up to the time of Newton.

There are numerous other books and web sites covering Galileo's work and the history of astronomy.

Questions

1. Why was the telescope an advance over naked-eye astronomy?

2. What did Galileo's observations of the Moon reveal?

3. What was the significance of Galileo observing phases of Venus?

4. How did Galileo's observations help undermine the existing paradigm of the Ptolemaic model of the Universe and Aristotle's physics?

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The science of astronomy took a huge leap forward in the first decade of the 1600s with the invention of the optical telescope and its use to study the night sky. Galileo Galilei did not invent the telescope but was the first to use it systematically to observe celestial objects and record his discoveries.

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Galieo Galilei was an Italian astronomer, physicist and mathematician who is widely credited as being the founder and father of modern science. Perhaps Galileo's biggest influence on today's science is that he was willing to stick to his findings despite the fact that the Catholic church felt he was in direct confrontation with their teachings. Galileo also made several advances in scientific fields and inventions which are still relied upon in some form or another to this day.

During Galileo's time the main way in which science was practiced still leaned heavily on "authority," meaning that whoever was the leading authority of that region provided the answers, and the public at large were expected to agree based mainly on faith. Galileo did not take statements at face value and investigated the causal effects of different variables. In effect, Galileo designed how experimentation would be carried out in the future.

Galileo changed the way mathematics was perceived by stressing that it was, in fact, the key to understanding how the world actually worked. His pioneering in this field allowed scientists like Sir Isaac Newton to build upon his work. Newton specifically used Galileo's work to help formulate his own laws of motion and explain how gravity works and affects objects.

While Galileo did not invent the first telescope, he did refine it to the point that he was able to see farther than any telescope of its time. This allowed him to see into outer space as well as set the basis for the kinds of powerful telescopes that we use today.

While Galileo was not the first scientist to posit that the earth actually revolved around the sun - along with the other planets - he is credited as being the one man who proved Copernicus' theory beyond a reasonable doubt. Using his telescope he was also able to demonstrate that the sun and the other planets were in fact naturally occurring bodies and not some sort of supernatural entities to be feared or mistrusted.

Since ancient Greece, scientists have attempted to measure the speed of light. With no way of measuring its speed, these ancient academics believed that the speed of light was practically limitless. However, in the early 17th Century, Galileo performed one of the earliest experiments to measure this by telling his assistant to cover and uncover lanterns at specific times while he reported on the light's appearance and disappearance from far away. While he concluded light was too fast to be measured, his experiment would pave the way to future experiments which would eventually result in discovering this incredibly fast velocity.

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Galieo Galilei was an Italian astronomer, physicist and mathematician who is widely credited as being the founder and father of modern science. Perhaps Galileo's biggest influence on today's science is that he was willing to stick to his findings despite the fact that the Catholic church felt he was in direct confrontation with their teachings.

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Discovered earth not the center of the universe.

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Discovered earth not the center of the universe.

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Dutch man made telescope; Galileo made one 32 times stronger.

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Italian astronomer and physicist Galileo Galilei is known as one of the great minds of science. During his lifetime, however, he was persecuted by the Catholic Church for his belief that the sun, not the Earth, is the center of the universe. Find out more about the iconic scientist, including whether or not he invented the telescope, what punishment he received after being tried by the Roman Inquisition and how his middle finger ended up in a museum.

He was a college dropout.

Galileo, whose father was a lute player and music theorist, was born in Pisa, Italy. Although his father was from a noble family, they weren't wealthy. As a preteen, Galileo began studying at a monastery near Florence and considered becoming a monk; however, his father wasn't in favor of his son pursuing a religious life and eventually removed him from the school. When he was 16, Galileo enrolled at the University of Pisa to study medicine, at his father's urging. Instead, though, he became interested in mathematics and shifted his focus to that subject. Galileo left the school in 1585 without earning a degree. He continued his mathematics studies on his own and earned money by giving private lessons before returning to the University of Pisa in 1589 to teach math.

He didn't invent the telescope.

Galileo didn't invent the telescope-Dutch eyeglass maker Hans Lippershey is generally credited with its creation-but he was the first person to use the optical instrument to systematically study the heavens. Lippershey's patent application for the device in 1608 is the earliest on record; however, because the Dutch government decided the telescope was too easy to copy and because another Dutch instrument-maker had tried to patent the device a short time after Lippershey, no patent was granted. In 1609, Galileo learned about the device and developed one of his own, significantly improving its design. That fall, he pointed it at the moon and discovered it had craters and mountains, debunking the common belief that the moon's surface was smooth.

Galileo soon went on to make other findings with his telescope, including that there were four moons orbiting Jupiter and that Venus went through a complete set of phases (indicating the planet traveled around the sun). Galileo's discoveries brought him acclaim and in 1610 he was named the chief mathematician and philosopher to the grand duke of Tuscany as well as chief mathematician at the University of Pisa. More significantly, Galileo's observations would lead him to support the theory, laid out in 1543 by Polish mathematician and astronomer Nicolaus Copernicus, that the sun is the center of the universe and the Earth and other planets revolve around it.

His daughters were nuns.

Galileo had three children with a woman named Marina Gamba, who he never married. In 1613, he placed his two daughters, Virginia, born in 1600, and Livia, born in 1601, in a convent near Florence, where they remained for the rest of their lives, despite their father's eventual troubles with the Catholic Church. Galileo maintained close ties with his older daughter, who became known as Sister Maria Celeste. From inside the convent, she baked and sewed for him, among other tasks. He in turn gave food and supplies to the impoverished convent. Galileo's son, Vincenzo, born in 1606, studied medicine at the University of Pisa, married well and resided in Florence as an adult.

Galileo was sentenced to life in prison by the Roman Inquisition.

Copernicus' heliocentric theory about the way the universe works challenged the widely accepted belief, espoused by the astronomer Ptolemy in the second century, that put the Earth at the center of the solar system. In 1616, the Catholic Church declared Copernican theory heretical because it was viewed as contradicting certain Bible verses. Galileo received permission from the Church to continue investigating Copernicus' ideas, as long as he didn't hold or defend them. In 1632, he published "Dialogue of the Two Principal Systems of the World," and although it was presented as a discussion between friends about the ideas of Ptolemy and Copernicus, the book was seen as supporting the Copernican model of the universe. As a result, the following year Galileo was ordered to stand trial before the Inquisition in Rome. After being found guilty of heresy, Galileo was forced to publicly repent and sentenced to life in prison.

He spent his final years under house arrest.

Although Galileo was given life behind bars, his sentence soon was changed to house arrest. He lived out his final years at Villa Il Gioiello ("the Jewel"), his home in the town of Arcetri, near Florence. Barred from seeing friends or publishing books, he nonetheless received visitors from around Europe, including philosopher Thomas Hobbes and poet John Milton. Additionally, he managed to smuggle out the manuscript for a new work, "Discourses and Mathematical Demonstrations Concerning Two New Sciences," about physics and mechanics. The book, Galileo's last, was published in Holland in 1638. That same year, Galileo went totally blind. He died on January 8, 1642, at age 77.

His middle finger is on display in a museum.

After Galileo died, he was buried in a side chapel at the church of Santa Croce in Florence. Nearly a century later, in 1737, as the scientist's remains were being transferred to a burial place of honor in the Santa Croce basilica three of his fingers, along with a vertebra and a tooth, were removed from his corpse. Two of Galileo's fingers, along with his tooth, were kept by one of his admirers and handed down through generations of his relatives. The items were thought to be lost sometime in the early 1900s. However, in 2009, the two fingers and tooth appeared at an auction and were snapped up by a private collector; using historical documentation, experts later concluded the items were Galileo's. Meanwhile, the third finger taken from Galileo's remains-the middle finger of his right hand-has been housed at various museums in Italy since at least the first half of the 1800s. The purloined vertebra ended up at the University of Padua, where Galileo taught from 1592 to 1610.

NASA named a spacecraft for him.

In 1989, NASA and a team from Germany launched a spacecraft bearing Galileo's name from the cargo bay of space shuttle Atlantis. After arriving at Jupiter in 1995, the Galileo spacecraft became the first to study the planet and its moons for an extended time. The spacecraft found evidence of saltwater below the surface of three of Jupiter's moons, Europa, Callisto and Ganymede, and provided information about volcanic activity on another one of the planet's moons, Io. (The four moons were discovered by the real-life Galileo in 1610 with a telescope.) In 2003, the mission came to an end when NASA intentionally crashed the spacecraft into Jupiter (the solar system's largest planet) in order to eliminate the risk of Galileo colliding with Europa and contaminating any potential life there.

The Vatican didn't admit Galileo was right until 1992.

In 1979, Pope John Paul II initiated an investigation into the Catholic Church's condemnation of Galileo. Thirteen years later, and 359 years after Galileo was tried by the Inquisition, the pope officially closed the investigation and issued a formal apology in the case, acknowledging that errors were made by the judges during the trial.

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Italian astronomer and physicist Galileo Galilei is known as one of the great minds of science. During his lifetime, however, he was persecuted by the Catholic Church for his belief that the sun, not the Earth, is the center of the universe.

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Sir Isaac Newton once wrote, in what must be one of the most oft-quoted lines in the history of science, "If I have seen further it is by standing upon the shoulders of giants." Well, any of us who has ever looked through a telescope could say the same, for the two principal types in use today were developed by giants: the refractor by Galileo and the reflector by Newton. Those two scientific geniuses, as Sir Isaac himself acknowledged, built upon the work of others, and how they came to design their inventions offers a compelling glance at the workings both of the telescope and of the scientific process itself.

Making the far near

The invention that set the stage for the telescope was the eyeglass, which appeared in the mid-13th century. The first spectacles, designed to correct farsightedness, bore glass magnifiers that were biconvex, meaning they curved outward on both sides. (Each resembled a lentil, or lens in Latin.) Mostly used to help older people read, these lenses focused on objects between 12 and 20 inches away from the eye.

Nearsightedness, a more common affliction, proved more difficult to correct. It required biconcave lenses-those curving inward on each surface-that had to bring objects into focus at the specific distance at which one's eyesight failed. The poorer one's vision, the greater the distance the lenses needed to provide focus.

In 1608, someone in Europe-it's not clear who-figured out that if you placed a lens for the farsighted about 12 to 14 inches away from a lens for the nearsighted, and then peered through the latter lens, distant objects would miraculously appear as if close by. (Oh, to have seen that pioneer's expression upon first realizing this!) Place those lenses in a tube and voilí , you have a spyglass.

Galileo also did what apparently no one else had ever done with a spyglass before: train the instrument on the heavens.

Within months, Galileo had not only learned of the new device but was well on his way to improving its design. In his workshop in Padua, Italy, he discovered that plano-convex and plano-concave lenses worked best-that is, lenses with a plane on one side and curved surfaces on the other. Then, drawing on his skills as a professor of mathematics at the University of Padua, he determined the mathematical relationship that governed the instrument's ability to magnify. A spyglass with a plano-convex lens that focuses at 12 inches and a plano-concave lens that focuses at four inches, he found, magnifies images three times (12 divided by four). Galileo played with this formula until, by the late fall of 1609, he'd made a spyglass that could magnify what is seen by 20 times. No other spyglass maker could match that.

That fall, Galileo also did what apparently no one else had ever done with a spyglass before: train the instrument on the heavens. In short order he began making astronomical findings that would shake our understanding of our place in the universe to its foundations. Among them was the discovery of four moons orbiting Jupiter. To Galileo, the moons proved that not everything in space circled the Earth, and therefore our planet was not the absolute center of the universe, as the Church maintained the Bible had it.

Building a better refractor

The spyglass-turned-telescope had limitations, some of which Galileo was able to design around. To reduce distortions such as elongations and blurriness caused by the curvature of the "objective" lens-the convex lens at the far end of the telescope-Galileo ground a lens larger than he needed, for example. He then placed cardboard around the edges of the lens so that light entered that portion of the lens where curvature-related distortions were least apparent.

Other problems Galileo would have to leave to others. One concerned magnification. In striving to make images he saw through his telescope ever larger, Galileo found that his field of view became ever smaller. He reached a point of diminishing returns beyond which enlarging the image made what was seen through the telescope too small to be of practical use. That point, he found, was achieved when he succeeded in magnifying the image 20 or 30 times.

Galileo's contemporary Johannes Kepler, a German mathematician, discovered a way to get beyond the magnification ceiling. Instead of a concave lens near the eye, Kepler used a convex lens. The result was that the image magnified by the convex objective lens was further magnified by the now-convex eyepiece lens. The only problem was that the resulting image was upside down. Some astronomers added a third convex lens to right the image, but this added unwanted distortions. Eventually, most astronomers simply accepted the inverted view. After all, did it really matter that they were seeing planets and stars upside down?

Designers of shorter telescopes still faced the problem of chromatic aberrations, though-that is, until Isaac Newton solved it.

Kepler's advance created a new challenge, however. Because his telescope offered a much greater field of view, astronomers had plenty of room to improve magnification. One way to do that, they knew, was to make the focal length of the eyepiece shorter. This, however, increased the curvature of the lens, which exacerbated the distracting fringes of color that surrounded images. The other way was to reduce the curvature of the objective lens. This results in fewer color problems, because the less a lens is curved the less it acts like a prism. But this made the focal length of the objective lens-and thus the instrument itself-longer. As Richard Panek writes in his book Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens, things got a little out of hand:

Six to eight feet-that was the length of a good astronomical telescope in 1645. Five years later it was 10 to 15 feet. Ten years after that, 25 feet. Ten years after that, 40 to 50 feet. By 1673, [Polish astronomer] Johannes Hevelius had constructed a telescope 150 feet long on the shores of the Baltic Sea....One astronomer cheered the coming day when aerial telescopes would have a focus of 1,000 feet and human spectators could marvel at the antics of the animals on the Moon.

Alas, extremely long telescopes proved to be impracticable. Most useful were those no longer than 30 or 40 feet-as Panek says, "long but not that long...."

Goodbye to color

Designers of shorter telescopes still faced the problem of chromatic aberrations, though-that is, until Isaac Newton solved it. In 1672, Newton published a seminal paper on light and color, in which he showed that white light is a mixture of all colors of the spectrum. When white light passes through a curved lens it breaks down into its various component colors, each of which comes into focus at a different point on the optical axis-hence the color fringes seen in refractors.

Other scientists had speculated that using mirrors rather than lenses might correct this problem, but Newton was the first to put such thoughts into practice. He cast a two-inch metal mirror and ground it so that it had a spherical curvature. He placed the mirror at one end of a tube. Light coming in the other end reflected off the mirror back toward the opening. The reflected light struck a secondary mirror Newton had affixed inside the tube at a 45-degree angle. That secondary mirror, in turn, bounced the light (and thus the image seen) into a convex eyepiece lens built into the side of the tube.

This was the first working reflecting telescope. Other designers proved unable to grind mirrors with a regular curvature, so the reflector remained largely a curiosity until the mid-18th century, when it finally began to come into its own.

Standing on shoulders

Both types of telescopes-Galileo's refractor and Newton's reflector-underwent improvements in the coming centuries. Designers of refracting telescopes figured out, for one, that by using two different kinds of glass together in the objective lens, they could cause the red and blue ends of the spectrum to converge towards a single focal point, thereby solving the color-fringe problem. Despite myriad embellishments, however, most optical telescopes in use in the 21st century derive from the two types developed in the 17th century by Galileo and Newton, on whose shoulders all astronomers, both amateur and professional, stand today.

Peter Tyson is editor in chief of NOVA Online.

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Sir Isaac Newton once wrote, in what must be one of the most oft-quoted lines in the history of science, "If I have seen further it is by standing upon the shoulders of giants."

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In 1610, Italian astronomer Galileo Galilei looked up at the heavens using a telescope of his making. And what he saw would forever revolutionize the field of astronomy, our understanding of the Universe, and our place in it. Centuries later, Galileo's is still held in such high esteem; not only for the groundbreaking research he conducted, but because of his immense ingenuity in developing his own research tools.

And at the center of it all is Galileo's famous telescope, which still inspires curiosity centuries later. How exactly did he invent it. How exactly was it an improvement on then-current designs? What exactly did he see with it when he looked up at the night sky? And what has become of it today? Luckily, all of these are questions we are able to answer.

Description:

Galileo's telescope was the prototype of the modern day refractor telescope. As you can see from this diagram below, which is taken from Galileo's own work - Sidereus Nuncius ("The Starry Messenger") - it was a simple arrangement of lenses that first began with optician's glass fixed to either end of a hollow cylinder.

Galileo had no diagrams to work from, and instead relied on his own system of trial and error to achieve the proper placement of the lenses. In Galileo's telescope the objective lens was convex and the eye lens was concave (today's telescopes make use of two convex lenses). Galileo knew that light from an object placed at a distance from a convex lens created an identical image on the opposite side of the lens.

He also knew that if he used a concave lens, the object would appear on the same side of the lens where the object was located. If moved at a distance, it appeared larger than the object. It took a lot of work and different arrangements to get the lens the proper sizes and distances apart, but Galileo's telescope remained the most powerful and accurately built for a great many years.

History of Galileo's Telescope:

Naturally, Galileo's telescope had some historical antecedents. In the late summer of 1608, a new invention was all the rage in Europe - the spyglass. These low power telescopes were likely made by almost all advanced opticians, but the very first was credited to Hans Lippershey of Holland. These primitive telescopes only magnified the view a few times over.

Much like our modern times, the manufacturers were quickly trying to corner the market with their invention. But Galileo Galilei's friends convinced his own government to wait - sure that he could improve the design. When Galileo heard of this new optical instrument he set about engineering and making improved versions, with higher magnification.

Galileo's telescope was similar to how a pair of opera glasses work - a simple arrangement of glass lenses to magnify objects. His first versions only improved the view to the eighth power, but Galileo's telescope steadily improved. Within a few years, he began grinding his own lenses and changing his arrays. Galileo's telescope was now capable of magnifying normal vision by a factor of 10, but it had a very narrow field of view.

However, this limited ability didn't stop Galileo from using his telescope to make some amazing observations of the heavens. And what he saw, and recorded for posterity, was nothing short of game-changing.

What Galileo Observed:

One fine Fall evening, Galileo pointed his telescope towards the one thing that people thought was perfectly smooth and as polished as a gemstone - the Moon. Imagine his surprise when found that it, in his own words, was "uneven, rough, full of cavities and prominences." Galileo's telescope had its flaws, such as a narrow field of view that could only show about one quarter of the lunar disk without repositioning.

Nevertheless, a revolution in astronomy had begun! Months passed, and Galileo's telescope improved. On January 7th, 1610, he turned his new 30 power telescope towards Jupiter, and found three small, bright "stars" near the planet. One was off to the west, the other two were to the east, and all three were in a straight line. The following evening, Galileo once again took a look at Jupiter, and found that all three of the "stars" were now west of the planet - still in a straight line!

And there were more discoveries awaiting Galileo's telescope: the appearance of bumps next to the planet Saturn (the edges of Saturn's rings), spots on the Sun's surface (aka. Sunspots), and seeing Venus change from a full disk to a slender crescent. Galileo Galilei published all of these findings in a small book titled Sidereus Nuncius ("The Starry Messenger") in 1610.

While Galileo was not the first astronomer to point a telescope towards the heavens, he was the first to do so scientifically and methodically. Not only that, but the comprehensive notes he took on his observations, and the publication of his discoveries, would have a revolutionary impact on astronomy and many other fields of science.

Galileo's Telescope Today:

Today, over 400 years later, Galileo's Telescope still survives under the constant care of the Istituto e Museo di Storia della Scienza (renamed the Museo Galileo in 2010) in Italy. The Museum holds exhibitions on Galileo's telescope and the observations he made with it. The displays consist of these rare and precious instruments - including the objective lens created by the master and the only two existing telescopes built by Galileo himself.

Thanks to Galileo's careful record keeping, craftsmen around the world have recreated Galileo's telescope for museums and replicas are now sold for amateurs and collectors as well. Despite the fact that astronomers now have telescopes of immense power at their disposal, many still prefer to go the DIY route, just like Galileo!

Few scientists and astronomers have had the same impact Galileo had. Even fewer are regarded as pioneers in the sciences, or revolutionary thinkers who forever changed humanity's perception of the heavens and their place within it. Little wonder then why his most prized instrument is kept so well preserved, and is still the subject of study over four centuries later.

We have written many interesting articles on Galileo here at Universe Today. Here's

Astronomy Cast also has an interesting episode on telescope making - Episode 327: Telescope Making, Part I

For more information, be sure to check out the Museo Galileo 's website.

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What is Galileo's Telescope? - Universe Today

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In 1610, Italian astronomer Galileo Galilei looked up at the heavens using a telescope of his making. And what he saw would forever revolutionize the field of astronomy, our understanding of the Universe, and our place in it.

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The Italian scientist turned his telescope toward the stars and changed our view of the universe

Inside a glass case was a plain-looking tube, worn and scuffed. Lying in the street, it would have looked like a length of old pipe. But as I approached it, Derrick Pitts-only half in jest-commanded: "Bow down!"

The unremarkable-looking object is in fact one of the most important artifacts in the history of science: it's one of only two surviving telescopes known to have been made by Galileo Galilei, the man who helped revolutionize our conception of the universe. The telescope was the centerpiece of "Galileo, the Medici and the Age of Astronomy," an exhibition at the Franklin Institute in Philadelphia in 2009.

Pitts, who runs the institute's planetarium and other astronomy programs, says that receiving the telescope from Florence's Galileo Museum-the first time the instrument ever left Florence-was "something of a religious experience." Understandably so: if Galileo is considered a patron saint of astronomy, then his telescope is one of its most holy relics. "Galileo's work with the telescope unleashed the notion that ours is a sun-centered solar system and not an Earth-centered solar system," says Pitts. In other words, from that ugly old cylinder came the profound idea that we are not the center of the universe.

It was a dangerous idea, and one that cost Galileo his freedom.

On a starry night in Padua 400 years ago, Galileo first turned a telescope toward the sky. It might seem the most natural of actions-after all,what else does one do with a telescope? But in 1609, the instrument, which had been invented only the year before by Dutch opticians, was known as a "spyglass," in anticipation of its military uses. The device was also sold as a toy. When Galileo read of it, he quickly set about making a much more powerful version. The Dutch telescopes magnified images by 3 times; Galileo's telescopes magnified them by 8 to 30 times.

At the time, astronomy, like much of science, remained under the spell of Aristotle. Almost 2,000 years after his death, the giant of Greek philosophy was held in such high regard that even his most suspect pronouncements were considered unimpeachable. Aristotle had maintained that all celestial objects were perfect and immutable spheres, and that the stars made a dizzying daily journey around the center of the universe, our stationary Earth. Why scrutinize the sky? The system had already been neatly laid out in books. Astronomers "wish never to raise their eyes from those pages," Galileo wrote in frustration, "as if this great book of the universe had been written to be read by nobody but Aristotle, and his eyes had been destined to see for all posterity."

In Galileo's day, the study of astronomy was used to maintain and reform the calendar. Sufficiently advanced students of astronomy made horoscopes; the alignment of the stars was believed to influence everything from politics to health.

Certain pursuits were not in an astronomer's job description, says Dava Sobel, author of the best-selling historical memoir Galileo's Daughter (1999). "You didn't talk about what the planets were made of," she says. "It was a foregone conclusion that they were made of the fifth essence, celestial material that never changed." Astronomers might make astrological predictions, but they weren't expected to discover anything new.

So when Galileo, then 45 years old, turned his telescope to the heavens in the fall of 1609, it was a small act of dissent. He saw that the Milky Way was in fact "a congeries of innumberable stars," more even than his tired hand could draw. He saw the pockmarked surface of the moon, which, far from being perfectly spherical, was in fact "full of cavities and prominences, being not unlike the face of the Earth." Soon he would note that Jupiter had four moons of its own and that Venus had moonlike phases, sometimes waxing to a disk, sometimes waning to a crescent. He later saw imperfections in the Sun. Each discovery drew Aristotle's system further into question and lent ever more support to the dangerously revolutionary view that Galileo had privately come to hold-set out just a half-century earlier by a Polish astronomer named Nicolaus Copernicus-that Earth traveled around the Sun.

"I give infinite thanks to God," Galileo wrote to the powerful Florentine statesman Belisario Vinta in January of 1610, "who has been pleased to make me the first observer of marvelous things."

Like many figures whose names have endured, Galileo wasn't shy about seeking fame. His genius for astronomy was matched by a genius for self-promotion, and soon, by virtue of several canny decisions, Galileo's own star was rising.

In Tuscany, the name Medici had been synonymous with power for centuries. The Medici family acquired and wielded it through various means-public office, predatory banking and alliances with the powerful Catholic Church. Conquest of territory was a method favored in the late 16th century, when the head of the family, Cosimo I, seized many regions neighboring Florence. The family took a keen interest in science and its potential military applications.

The Medicis may have needed scientists, but scientists-and especially Galileo-needed the Medicis even more. With a mistress, three children and an extended family to support, and knowing that his questioning of Aristotelian science was controversial, Galileo shrewdly decided to court the family's favor. In 1606, he dedicated a book about a geometric and military compass to his student Cosimo II, the family's 16-year-old heir apparent.

Then, in 1610, on the occasion of his publication of The Starry Messenger, which detailed his telescopic findings, Galileo dedicated to Cosimo II something far greater than a book: the very moons of Jupiter. "Behold, therefore, four stars reserved for your illustrious name," wrote Galileo. "...Indeed it appears that the Maker of the Stars himself, by clear arguments, admonished me to call these new planets by the illustrious name of Your Highness before all others." (Galileo chose the name "Cosmian stars," but Cosimo's office requested "Medicean stars" instead, and the alteration was duly made.) " The Starry Messenger was a job application," says Owen Gingerich, an astronomer and science historian at the Harvard-Smithsonian Center for Astrophysics-and, sure enough, Galileo got just what he had been seeking: the Medicis' patronage.

He could hardly have hoped for better patrons, as the Franklin exhibit made clear. It included scores of intricately wrought instruments from the family's collection. The fanciful names of the ingenious contraptions hint at their function and describe their forms: nautical planispheres, gimbaled compasses, horary quadrants, armillary spheres. One of the oldest surviving astrolabes, an instrument for calculating the position of the Sun and stars, was on exhibit, as was a set of brass and steel compasses believed to have belonged to Michelangelo, another Medici beneficiary. (Galileo's telescope and the rest of the collection have since returned to Florence.)

Though capable of measuring the world in various ways and to various ends-determining the caliber of projectiles, surveying land, aiding navigation-some of the instruments were never used, having been collected for the very purpose to which museums put them today: display. A few, such as a compass that collapses into the shape of a dagger, demonstrate the era's alliance of science and power. But they also illustrate its blending of science and art-the gleaming artifacts rival works of sculpture. They tell, too, of a growing awareness that, as Galileo said, nature was a grand book (" questo grandissimo libro") written in the language of mathematics.

Not everyone took pleasure in-or even believed-what Galileo claimed to have seen in the sky.

Some of his contemporaries refused to even look through the telescope at all, so certain were they of Aristotle's wisdom. "These satellites of Jupiter are invisible to the naked eye and therefore can exercise no influence on the Earth, and therefore would be useless, and therefore do not exist," proclaimed nobleman Francesco Sizzi. Besides, said Sizzi, the appearance of new planets was impossible-since seven was a sacred number: "There are seven windows given to animals in the domicile of the head: two nostrils, two eyes, two ears, and a mouth....From this and many other similarities in Nature, which it were tedious to enumerate, we gather that the number of planets must necessarily be seven."

Some who did deign to use the telescope still disbelieved their own eyes. A Bohemian scholar named Martin Horky wrote that "below, it works wonderfully; in the sky it deceives one." Others nominally honored the evidence of the telescope but scrambled to make it conform to their preconceptions. A Jesuit scholar and correspondent of Galileo named Father Clavius attempted to rescue the idea that the Moon was a sphere by postulating a perfectly smooth and invisible surface stretching above its scarred hills and valleys.

The Starry Messenger was a success, however: the first 500 copies sold out within months. There was a great demand for Galileo's telescopes, and he was named the head mathematician at the University of Pisa.

In time Galileo's findings began to trouble a powerful authority-the Catholic Church. The Aristotelian worldview had been integrated with Catholic teachings, so any challenges to Aristotle had the potential to run afoul of the church. That Galileo had revealed flaws in celestial objects was bothersome enough. But some of his observations, especially the changing phases of Venus and the presence of moons around other planets, lent support to Copernicus' heliocentric theory, and that made Galileo's work potentially heretical. Biblical literalists pointed to the book of Joshua, in which the Sun is described as stopping, miraculously, "in the midst of heaven, and hasted not to go down about a whole day." How could the Sun stop if, as Copernicus and now Galileo claimed, it was already stationary? By 1614, a Dominican friar named Tommaso Caccini preached openly against Galileo, calling the Copernican worldview heretical. In 1615 another Dominican friar, Niccolò Lorini, filed a complaint against Galileo with the Roman Inquisition, a tribunal instituted the previous century to eliminate heresy.

These church challenges greatly troubled Galileo, a deeply pious man. It is a common misconception that Galileo was irreligious, but as Dava Sobel says, "Everything he did, he did as a believing Catholic." Galileo simply believed that Scripture was not intended to teach astronomy, but rather, as he wrote in a 1613 letter to his disciple Benedetto Castelli, to "persuade men of the truths necessary for salvation." Some members of the church held the same opinion: Cardinal Baronius in 1598 said that the Bible was meant "to teach us how to go to heaven, not how the heavens go."

Late in 1615, Galileo traveled to Rome to meet with church leaders personally; he was eager to present his discoveries and make the case for heliocentrism. But Baronius' view turned out to be the minority one in Rome. Galileo was cautioned against defending Copernicanism.

Eight years later, a new pope, Urban VIII, ascended and Galileo again requested permission to publish. Pope Urban granted permission-with the caveat that Galileo present the theory as a hypothesis only. But the book Galileo finally published in 1632, Dialogue Concerning the Two Chief World Systems, came off clearly in favor of the Copernican view, infuriating the pope.

And so, in what Pope John Paul II would deem, more than three centuries later, a case of "tragic mutual incomprehension," Galileo was condemned by the Holy Office of the Inquisition for being "vehemently suspected of heresy, namely of having held and believed the doctrine which is false and contrary to the Sacred and Divine Scriptures, that the Sun is the center of the world." He was sentenced to imprisonment, which was commuted to house arrest for the by then ailing 69-year-old man.

Despite repeated requests for clemency, the astronomer spent his last eight years confined to his home, forbidden to speak or write of the topics that had so captivated him. (Meanwhile, forbidden copies of his Dialogue are thought to have been widely sold on the black market.) Blindness overcame him, and as he wrote to a friend in 1638, "The universe which I with my astonishing observations and clear demonstrations had enlarged a hundred, nay, a thousandfold beyond the limits commonly seen by wise men of all centuries past, is now for me so diminished and reduced, it has shrunk to the meager confines of my body."

The exact composition of some of Galileo's telescopes remains a mystery. A written fragment-a shopping list jotted on a letter-allows historians to surmise the materials Galileo used for his lenses. And so the ingredients for one of the most famous telescopes in history-an organ pipe, molds for shaping lenses, abrasives for polishing glass-are thrown in with reminders to buy soap, combs and sugar.

It's a humdrum list-as plain as the lusterless tube in a museum display. Yet what came from that tube, like the man who made it, was anything but ordinary. Galileo "was one of those who was present at the birth of modern astronomy," says Harvard-Smithsonian's Gingerich.

In the dedication of The Starry Messenger, addressed to Cosimo II, Galileo hailed the effort to "preserve from oblivion and ruin names deserving of immortality." But the moons of Jupiter he named the Medicean have come to be more commonly known as the Galilean moons, and in 1989, the spacecraft NASA launched to study them was named Galileo. And 2009 was named the International Year of Astronomy by the United Nations in honor of the 400th anniversary of Galileo's first telescopic observations.

The fame Galileo sought and obtained, he earned. "Galileo understood what was fundamentally important" about his telescopic observations, says Gingerich. "Namely, that they were showing us a whole new universe."

David Zax has written for Smithsonian about Elvis in the Army, a party of Santas and George Washington's boyhood home.

About David Zax

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Galileo's Revolutionary Vision Helped Usher In Modern Astronomy

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Inside a glass case was a plain-looking tube, worn and scuffed. Lying in the street, it would have looked like a length of old pipe. But as I approached it, Derrick Pitts-only half in jest-commanded: "Bow down!"

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Italian astronomer Galileo Galilei provided a number of scientific insights that laid the foundation for future scientists. His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time - that all things revolved around the Earth.

[See also our overview of Famous Astronomers and great scientists from many fields who have contributed to the rich history of discoveries in astronomy.]

Galileo's experiments

The Ancient Greek philosopher, Aristotle, taught that heavier objects fall faster than lighter ones, a belief still held in Galileo's lifetime. But Galileo wasn't convinced. Experimenting with balls of different sizes and weights, he rolled them down ramps with various inclinations. His experiments revealed that all of the balls boasted the same acceleration independent of their mass. He also demonstrated that objects thrown in the air travel along a parabola.

At the same time, Galileo worked with pendulums. In his life, accurate timekeeping was virtually nonexistent. Galileo observed, however, that the steady motion of a pendulum could improve this. In 1602, he determined that the time it takes a pendulum to swing back and forth does not depend on the arc of the swing. Near the end of his lifetime, Galileo designed the first pendulum clock.

Galileo's telescope

Galileo is often incorrectly credited with the creation of a telescope. ( Hans Lippershey applied for the first patent in 1608, but others may have beaten him to the actual invention.) Instead, he significantly improved upon them. In 1609, he first learned of the existence of the spyglass, which excited him. He began to experiment with telescope-making, going so far as to grind and polish his own lenses. His telescope allowed him to see with a magnification of eight or nine times. In comparison, spyglasses of the day only provided a magnification of three.

It wasn't long before Galileo turned his telescope to the heavens. He was the first to see craters on the moon, he discovered sunspots, and he tracked the phases of Venus. The rings of Saturn puzzled him, appearing as lobes and vanishing when they were edge-on - but he saw them, which was more than can be said of his contemporaries.

Of all of his telescope discoveries, he is perhaps most known for his discovery of the four most massive moons of Jupiter, now known as the Galilean moons: Io, Ganymede, Europa and Callisto. When NASA sent a mission to Jupiter in the 1990s, it was called Galileo in honor of the famed astronomer.

In his book " Sidereus Nuncius" ("Starry Messenger"), published in 1610, Galileo wrote:

"On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavens through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, namely that three little stars, small but very bright, were near the planet; and although I believed them to belong to a number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude . . . When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night."

"I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury around the Sun; which was at length established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter."

Galileo may also have made the first recorded studies of the planet Neptune, though he didn't recognize it as a planet. While observing Jupiter's moons in 1612 and 1613, he recorded a nearby star whose position is not found in any modern catalogues.

"It has been known for several decades that this unknown star was actually the planet Neptune," University of Melbourne physicist David Jamieson told Space.com. "Computer simulations show the precision of his observations revealing that Neptune would have looked just like a faint star almost exactly where Galileo observed it."

Copernican system

In Galileo's lifetime, all celestial bodies were thought to orbit the Earth. Supported by the Catholic Church, teaching opposite of this system was declared heresy in 1615.

Galileo, however, did not agree. His research - including his observations of the phases of Venus and the fact that Jupiter boasted moons that didn't orbit Earth - supported the Copernican system, which (correctly) stated that the Earth and other planets circle the sun.

In 1616, he was summoned to Rome and warned not to teach or write about this controversial theory. But in 1632, believing that he could write on the subject if he treated it as a mathematical proposition, he published work on the Copernican system. He was found guilty of heresy, and was placed under house arrest for the remaining nine years of his life.

Galileo quotes

"And yet it moves."

"I have never met a man so ignorant that I couldn't learn something from him."

"I do 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."

"You cannot teach a man anything, you can only help him find it within himself."

"It is a beautiful and delightful sight to behold the body of the Moon."

"Wine is sunlight, held together by water."

- Find other quotes at GoodReads.com.
Additional resources

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Galileo Galilei: Biography, Inventions & Other Facts

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Italian astronomer Galileo Galilei provided a number of scientific insights that laid the foundation for future scientists. His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time - that all things revolved around the Earth.

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Life

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Wow!

Galileo discovered four of Jupiter's moons almost four hundred years ago.

Galileo Galilei was an Italian physicist and astronomer. He was born in Pisa on February 15, 1564. Galileo's father, Vincenzo Galilei, was a well-known musician. Vincenzo decided that his son should become a doctor.

In 1581, Galileo was sent to the University of Pisa to study medicine. While a student at the university, Galileo discovered that he had a talent for mathematics. He was able to persuade his father to allow him to leave the university to become a tutor in mathematics. He later became a professor of mathematics.

In 1609, Galileo heard about the invention of the spyglass, a device which made distant objects appear closer. Galileo used his mathematics knowledge and technical skills to improve upon the spyglass and build a telescope. Later that same year, he became the first person to look at the Moon through a telescope and make his first astronomy discovery. He found that the Moon was not smooth, but mountainous and pitted - just like the Earth! He subsequently used his newly invented telescope to discover four of the moons circling Jupiter, to study Saturn, to observe the phases of Venus, and to study sunspots on the Sun.

Galileo's observations strengthened his belief in Copernicus' theory that Earth and all other planets revolve around the Sun. Most people in Galileo's time believed that the Earth was the center of the universe and that the Sun and planets revolved around it.

The Catholic Church, which was very powerful and influential in Galileo's day, strongly supported the theory of a geocentric, or Earth-centered, universe. After Galileo began publishing papers about his astronomy discoveries and his belief in a heliocentric, or Sun-centered, Universe, he was called to Rome to answer charges brought against him by the Inquisition (the legal body of the Catholic Church). Early in 1616, Galileo was accused of being a heretic, a person who opposed Church teachings. Heresy was a crime for which people were sometimes sentenced to death. Galileo was cleared of charges of heresy, but was told that he should no longer publicly state his belief that Earth moved around the Sun. Galileo continued his study of astronomy and became more and more convinced that all planets revolved around the Sun. In 1632, he published a book that stated, among other things, that the heliocentric theory of Copernicus was correct. Galileo was once again called before the Inquisition and this time was found guilty of heresy. Galileo was sentenced to life imprisonment in 1633. Because of his age and poor health, he was allowed to serve his imprisonment under house arrest. Galileo died on January 8, 1642.

A Question

Why did the Inquisition sentence Galileo to life imprisonment?

The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC.

StarChild Authors: The StarChild Team
StarChild Graphics & Music: Acknowledgments
StarChild Project Leader: Dr. Laura A. Whitlock
Curator:J.D. Myers
Responsible NASA Official: Phil Newman

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Wow! Galileo discovered four of Jupiter's moons almost four hundred years ago. Galileo Galilei was an Italian physicist and astronomer. He was born in Pisa on February 15, 1564. Galileo's father, Vincenzo Galilei, was a well-known musician. Vincenzo decided that his son should become a doctor.

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Who Was Galileo?

Galileo was an Italian astronomer, mathematician, physicist, philosopher and professor who made pioneering observations of nature with long-lasting implications for the study of physics.

He also constructed a telescope and supported the Copernican theory, which supports a sun-centered solar system. Galileo was accused twice of heresy by the church for his beliefs, and wrote a number of books on his ideas.

Early Life

Galileo Galilei was born in Pisa in the Duchy of Florence, Italy, on February 15, 1564.

Galileo was the first of six children born to Vincenzo Galilei, a well-known musician and music theorist, and Giulia Ammannati. In 1574, the family moved to Florence, where Galileo started his formal education at the Camaldolese monastery in Vallombrosa.

Education

In 1583, Galileo entered the University of Pisa to study medicine. Armed with prodigious intelligence and drive, he soon became fascinated with many subjects, particularly mathematics and physics.

While at Pisa, Galileo was exposed to the Aristotelian view of the world, then the leading scientific authority and the only one sanctioned by the Roman Catholic Church.

At first, Galileo supported this view, like any other intellectual of his time, and was on track to be a university professor. However, due to financial difficulties, Galileo left the university in 1585 before earning his degree.

Career as a Professor

Galileo continued to study mathematics after leaving the university, supporting himself with minor teaching positions.

During this time he began his two-decade study on objects in motion and published The Little Balance, describing the hydrostatic principles of weighing small quantities, which brought him some fame. This gained him a teaching post at the University of Pisa, in 1589.

While there, Galileo conducted his fabled experiments with falling objects and produced his manuscript Du Motu (On Motion), a departure from Aristotelian views about motion and falling objects. Galileo developed an arrogance about his work, and his strident criticisms of Aristotle left him isolated among his colleagues. In 1592, his contract with the University of Pisa was not renewed.

Galileo quickly found a new position at the University of Padua, teaching geometry, mechanics and astronomy. The appointment was fortunate, for his father had died in 1591, leaving Galileo entrusted with the care of his younger brother.

During his 18-year tenure at Padua, he gave entertaining lectures and attracted large crowds of followers, further increasing his fame and his sense of mission.

Daughters and Son

In 1600, Galileo met Marina Gamba, a Venetian woman, who bore him three children out of wedlock: daughters Virginia and Livia, and son Vincenzo. He never married Marina, possibly due to financial worries and possibly fearing his illegitimate children would threaten his social standing.

Galileo worried his daughters would never marry well, and when they were older, had them enter a convent. In 1616, at the San Mateo Convent, Virginia changed her name to Maria Celeste and Livia became Sister Arcangela, when they became nuns. Maria Celeste remained in contact and supported her father through letters until her death.

No letters from Arcangela survive. His son's birth was eventually legitimized and he became a successful musician.

Telescope

In July 1609, Galileo learned about a simple telescope built by Dutch eyeglass makers and soon developed one of his own. In August, he demonstrated it to some Venetian merchants, who saw its value for navigation and spotting ships. The merchants gave Galileo a salary to manufacture several of them.

Galileo's ambition pushed him to go further, and in the fall of 1609 he made the fateful decision to turn his telescope toward the heavens. Using his telescope to explore the universe, Galileo observed the moon and found Venus had phases like the moon, proving it rotated around the sun, which refuted the Aristotelian doctrine that the Earth was the center of the universe.

He also discovered Jupiter had revolving moons that didn't revolve around planet Earth. In 1613, he published his observations of sunspots, which also refuted Aristotelian doctrine that the sun was perfect.

Books

Galileo published a number of books throughout his career, including:

The Operations of the Geometrical and Military Compass (1604), which revealed Galileo's skills with experiments and practical technological applications.

The Starry Messenger (1610), a small booklet revealing Galileo's discoveries that the moon was not flat and smooth but a sphere with mountains and craters.

Discourse on Bodies in Water (1612), which refuted the Aristotelian explanation of why objects float in water, saying that it wasn't because of their flat shape, but instead the weight of the object in relation to the water it displaced.

Dialogue Concerning the Two Chief World Systems (1632), a discussion among three people: one who supports Copernicus' heliocentric theory of the universe, one who argues against it, and one who is impartial. Though Galileo claimed Dialogues was neutral, it was clearly not. The advocate of Aristotelian belief comes across as the simpleton, getting caught in his own arguments.

Two New Sciences (1638), a summary of Galileo's life's work on the science of motion and strength of materials.

What Did Galileo Discover?

In addition to the telescope and his numerous mathematical and scientific discoveries, in 1604 Galileo constructed a hydrostatic balance for measuring small objects.

That same year, he also refined his theories on motion and falling objects, and developed the universal law of acceleration, which all objects in the universe obeyed. He also devised a type of simple thermometer.

Thermometer

A simple glass-bulb thermometer known as a Galileo thermometer wasn't invented by Galileo, but was based on his understanding that the density of liquids changes based on its temperature.

A thermoscope that Galileo designed (or helped to design) is similar to modern-day thermometers. Inside the thermoscope, a liquid rises and falls in a glass tube as the temperature of the liquid rises or falls.

DOWNLOAD BIOGRAPHY'S GALILEO FACT CARD

Galileo and the Church

After Galileo built his telescope in 1609, he began mounting a body of evidence and openly supporting the Copernican theory that the earth and planets revolve around the sun. The Copernican theory, however, challenged the doctrine of Aristotle and the established order set by the Catholic Church.

In 1613, Galileo wrote a letter to a student to explain how Copernican theory did not contradict Biblical passages, stating that scripture was written from an earthly perspective and implied that science provided a different, more accurate perspective.

The letter was made public and Church Inquisition consultants pronounced Copernican theory heretical. In 1616, Galileo was ordered not to "hold, teach, or defend in any manner" the Copernican theory. Galileo obeyed the order for seven years, partly to make life easier and partly because he was a devoted Catholic.

In 1623, a friend of Galileo, Cardinal Maffeo Barberini, was elected as Pope Urban VIII. He allowed Galileo to pursue his work on astronomy and even encouraged him to publish it, on condition it be objective and not advocate Copernican theory. This led Galileo to publish Dialogue Concerning the Two Chief World Systems in 1632, which advocated the theory.

Church reaction was swift, and Galileo was summoned to Rome. Galileo's Inquisition proceedings lasted from September 1632 to July 1633. During most of this time, Galileo was treated with respect and never imprisoned.

However, in a final attempt to break him, Galileo was threatened with torture, and he finally admitted he had supported Copernican theory, but privately held that his statements were correct. He was convicted of heresy and spent his remaining years under house arrest.

Though ordered not to have any visitors nor have any of his works printed outside of Italy, he ignored both. In 1634, a French translation of his study of forces and their effects on matter was published, and a year later, copies of the Dialogue were published in Holland.

While under house arrest, Galileo wrote Two New Sciences, published in Holland in 1638. By this time, Galileo had become blind and was in poor health.

In time, however, the Church couldn't deny the truth in science. In 1758, it lifted the ban on most works supporting Copernican theory. It wasn't until 1835 that the Vatican dropped its opposition to heliocentrism altogether.

In the 20th century, several popes acknowledged the great work of Galileo, and in 1992, Pope John Paul II expressed regret about how the Galileo affair was handled.

How Did Galileo Die?

Galileo died after suffering from a fever and heart palpitations on January 8, 1642, in Arcetri, near Florence, Italy.

Galileo's contribution to our understanding of the universe was significant not only for his discoveries, but for the methods he developed and the use of mathematics to prove them. He played a major role in the Scientific Revolution and earned the title "The Father of Modern Science."

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Galileo was an Italian astronomer, mathematician, physicist, philosopher and professor who made pioneering observations of nature with long-lasting implications for the study of physics. He also constructed a telescope and supported the Copernican theory, which supports a sun-centered solar system.

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Many consider G = father of modern science