Galileo Galilei and Telescopic Astronomy

As the first astronomer to use a telescope to view the heavens, the Italian scientist Galileo Galilei (1564-1642) conducted early astronomical observations that helped inflame the Scientific Revolution of the 17th century. In 1610 he announced some of his early telescopic findings in the publication Starry Messenger, including the discovery of the four major moons of Jupiter (now called the Galilean satellites). The fact that they behaved like

GALILEO

PLANETARY 08SERVATI0NS-161Q

DRAWINGS OF PLANETS GALILEO IN 1G40

A 1640 portrait of Galileo Galilei—the fiery Italian astronomer, physicist, and mathematician who used his own version of the newly invented telescope to make detailed astronomical observations that helped inflame the Scientific Revolution in the 17th century. (NASA)

DRAWINGS OF PLANETS GALILEO IN 1G40

A 1640 portrait of Galileo Galilei—the fiery Italian astronomer, physicist, and mathematician who used his own version of the newly invented telescope to make detailed astronomical observations that helped inflame the Scientific Revolution in the 17th century. (NASA)

a miniature solar system stimulated his enthusiastic support for the heliocentric cosmology of Nicholas Copernicus (1473-1543). Unfortunately, this scientific work led to a direct clash with ecclesiastical authorities, who insisted on retaining the Ptolemaic system (with its geocentric cosmology) for a number of political and social reasons. By 1632 this conflict earned the fiery Galileo an Inquisition trial at which he was found guilty of heresy (for advocating the Copernican system) and confined to house arrest for the remainder of his life.

Galileo Galilei was born in Pisa on February 15, 1564. (Scientists and astronomers commonly refer to Galileo by only his first name). When he entered the University of Pisa in 1581, his father encouraged him to study medicine. His inquisitive mind soon became more interested in physics and mathematics than medicine. While still a medical student, he attended church services one Sunday. During the sermon, he noticed a chandelier swinging in the breeze and began to time its swing using his own pulse as a crude clock. When he returned home, he immediately set up an experiment that revealed the pendulum principle. After just two years of study, Galileo abandoned medicine and focused on mathematics and science. His change in career pathways also changed the entire trajectory of science.

In 1585 Galileo left the university without receiving a degree and focused his activities on the physics of solid bodies. The motion of falling objects and projectiles intrigued him. Then, in 1589, he became a mathematics professor at the University of Pisa. Galileo was a brilliant lecturer and students came from all over Europe to attend his classrooms. This circumstance quickly angered many senior, but less capable, faculty members. To make matters worse, Galileo often used his tenacity, sharp wit, and biting sarcasm to win philosophical arguments at the university. His tenacious and argumentative personality earned him the nickname "The Wrangler."

In the late 16th century, European professors usually taught physics (then called natural philosophy) as an extension of Aristotelian philosophy and not as an observational, experimental science. Through his skillful use of mathematics and innovative experiments, Galileo changed that approach. His activities constantly challenged the 2,000-year tradition of ancient Greek learning. For example, Aristotle stated that heavy objects would fall faster then lighter objects. Galileo disagreed and held the opposite view that, except for air resistance, the two objects would fall at the same time regardless of their masses. Historians are not certain whether he personally performed the legendary musket ball-cannon ball drop experiment from the Leaning Tower in Pisa to prove this point. However, he did conduct a sufficient number of experiments with objects on inclined planes to upset Aristotelian physics and create the science of mechanics.

Throughout his life, Galileo was limited in his motion experiments by an inability to accurately measure small increments of time. Despite this impediment, he conducted many important experiments that produced remarkable insights into the physics of free fall and projectile motion. Less than a century later, Sir Isaac Newton (1642-1727) would build upon Galileo's work to create the universal law of gravitation and three laws of motion—the pillars of classical physics.

By 1592 Galileo's anti-Aristotelian research and abrasive behavior had offended his colleagues at the University of Pisa so much that they not so politely invited him to teach elsewhere. Later that year, Galileo moved to the University of Padua. This university had a more lenient policy of academic freedom, encouraged in part by the progressive government of the Republic of Venice. In Padua Galileo wrote a special treatise on mechanics to accompany his lectures. He also began teaching courses on geometry and astronomy. (At the time, the university's astronomy courses were primarily for medical students who needed to learn about what was known as medical astrology.)

In 1597 the German astronomer Johannes Kepler provided Galileo with a copy of Copernicus's book (even though the book was officially banned in Italy). Although Galileo had not previously been interested in astronomy, he discovered and immediately embraced the Copernican model. Galileo and Kepler continued to correspond until about 1610.

Between 1604 and 1605, Galileo performed his first public work involving astronomy. He observed the supernova of 1604 (in the constellation Ophiuchus) and used this astronomical event to refute the cherished Aristotelian belief that the heavens were immutable (unchangeable). He delivered this challenge on Aristotle's doctrine in a series of public lectures. Unfortunately, these well-attended lectures brought him into direct conflict with many of the university's pro-Aristotelian philosophy professors.

In 1609 Galileo learned that a new optical instrument (a magnifying tube) had just been invented in Holland. Within six months, Galileo devised his own version of the instrument. Then, in 1610, he turned this improved telescope to the heavens and started the age of telescopic astronomy. With his crude instrument, he made a series of astounding discoveries, including mountains on the Moon, many new stars, and the four major moons of Jupiter—now called the Galilean satellites in his honor. Galileo published these important discoveries in the book Sidereus Nuncius (Starry messenger). The book stimulated both enthusiasm and anger. Galileo used the moons of Jupiter to prove that not all heavenly bodies revolve around Earth. This provided direct observational evidence for the Copernican model—a cosmological model that Galileo now vigorously endorsed.

Birth of a Neutron Star and Supernova Remnant

(not to scale)

Birth of a Neutron Star and Supernova Remnant

(not to scale)

Core Implosion Supernova Explosion Supernova Remnant

This is an artist's rendering that depicts the birth of a neutron star following a supernova explosion. (NASA/CXC)

Core Implosion Supernova Explosion Supernova Remnant

Supernovas

About once every 50 or so years, a massive star in the Milky Way Galaxy blows itself apart in a spectacular supernova explosion. Scientists regard supernovas as one of the most violent events in the universe. The force of a supernova explosion generates a blinding flash of radiation, as well as shock waves through interstellar space that are analogous to sonic booms. (Note that this is just a useful analogy, since sound waves cannot propagate through the vacuum of outer space.) Based on spectral classification activities in the 1930s, astrophysicists came to divide supernovas into two basic physical types: Type Ia and Type II. This classification is still used.

The Type Ia supernova involves the sudden explosion of a white dwarf star in a binary star system. A white dwarf is the evolutionary endpoint for stars with masses up to about five times the mass of the Sun. The remaining white dwarf has a mass of about 1.4 times the mass of the Sun and is about the size of Earth. A white dwarf in a binary star system will draw material off its stellar companion, if the two stars orbit close to each other. Mass capture hap

This is an artist's rendering that depicts the birth of a neutron star following a supernova explosion. (NASA/CXC)

pens because the white dwarf is a very dense object and exerts a very strong gravitational pull. Should the in-falling matter from a suitable companion star, such as a red giant, cause the white dwarf to exceed 1.4 solar masses (the Chandrasekhar limit), the white dwarf begins to experience gravitational collapse and creates internal conditions sufficiently energetic to support the thermonuclear fusion of elements like carbon. The carbon and other elements that make up the white dwarf begin to fuse uncontrollably, resulting in an enormous thermonuclear explosion that involves and consumes the entire star. Astronomers sometimes call this type of supernova a carbon-detonation supernova.

Unable to continue teaching old doctrine at the university, Galileo left Padua in 1610 and went to Florence. There he accepted an appointment as chief mathematician and philosopher to the grand duke of Tuscany, Cosimo II. He resided in Florence for the remainder of his life.

Because of Sidereus Nuncius, Galileo's fame spread throughout Italy and the rest of Europe. His telescopes were in demand, and he obligingly provided them to select European astronomers, including Kepler. In 1611

The Type II supernova is also called the massive star supernova. Stars that are five times or more massive than the Sun end their lives in a most spectacular way. The process starts when there is no longer enough fuel for the fusion process to occur in the core. When a star is functioning normally and in equilibrium, fusion takes place in its core, and the energy liberated by the thermonuclear reactions produces an outward pressure that combats the inward gravitational attraction of the star's great mass. But when a massive star that is going to become a supernova begins to die, it first swells into a red giant or supergiant—at least on the outside. In the interior, its core begins shrinking. As the star's core shrinks, the material becomes hotter and denser. Under these extremely heated and compressed conditions, a new series of thermonuclear reactions takes place, involving elements all the way up to, but not including, iron (Fe). Energy released from these fusion reactions temporarily halts the further collapse of the core.

However, this pause in the gravity-driven implosion of the core is only temporary. When the compressed core contains essentially only iron, all fusion ceases. (From nuclear physics, scientists know that iron nuclei are extremely stable and cannot fuse into higher atomic number elements.). At this point, the dying star begins the final phase of gravitational collapse. In less than a second, the core temperature rises to over 100 billion degrees Fahrenheit (55 billion degrees Celsius), as the iron nuclei are quite literally crushed together by the unrelenting influence of gravitational attraction. Then, this atom-crushing collapse abruptly halts due to the buildup of neutron pressure in the degenerate core material. The collapsing core recoils as it encounters this neutron pressure, and a rebound shock wave travels outward through the overlying material. The passage of this intense shock causes numerous nuclear reactions in the overlying outer material of the red giant, and the end result is a gigantic explosion. The shock wave also propels remnants of the original overlying material and any elements synthesized by various nuclear reactions out into space.

All but the central neutron star is blown away at speeds in excess of 31 million miles (50 million km) per hour. A thermonuclear shock wave races through the now-expanding stellar debris, fusing lighter elements into heavier ones and producing a brilliant visual outburst that appears as intense as the light of several billion Suns. Astronomers call the material that is exploded out into space a supernova remnant.

All that remains of the original star is a small, super-dense core composed almost entirely of neutrons—a neutron star. Because of the sequence of physical processes just mentioned, astrophysicists sometimes call a Type II supernova an implosion-explosion supernova. If the original star was very massive (perhaps 15 or more solar masses), even neutrons are not able to withstand the relentless collapse of the core's degenerate matter, and a black hole forms.

he proudly took one of his telescopes to Rome and let church officials personally observe some of these amazing celestial discoveries. While in Rome, he also became a member of the prestigious Academia dei Lincei (Lyncean academy). Founded in 1603, the academy was the world's first true scientific society.

In 1613 Galileo published his "Letters on Sunspots" through the academy. He used the existence and motion of sunspots to demonstrate that the Sun itself changes, again attacking Aristotle's doctrine of the immutability of the heavens. In so doing, he also openly endorsed the Copernican model. This started Galileo's long and bitter fight with ecclesiastical authorities. Above all, Galileo believed in the freedom of scientific inquiry. Late in 1615, Galileo went to Rome and publicly argued for the Copernican model. This public action angered Pope Paul V, who immediately formed a special commission to review the theory of Earth's motion.

Dutifully, the (unscientific) commission concluded that the Copernican theory was contrary to biblical teachings and possibly a form of heresy. Cardinal Robert Bellarmine (an honorable person who was later canonized) received the unenviable task of silencing the brilliant, but stubborn, Galileo. In late February 1616, he officially admonished Galileo to abandon his support of the Copernican hypothesis. Acting under direct orders from Pope Paul V, the cardinal made Galileo an offer he could not refuse. Galileo must never teach or write again about the Copernican model or else he would be tried for heresy and then imprisoned or possibly executed, like Giordano Bruno (1548-1600).

Apparently, Galileo got the mes-sage—at least so it seemed for a few years. In 1623 he published Il Saggiatore (The assayer). In this book, he discussed the principles for scientific research but carefully avoided support for Copernican theory. He even dedicated the book to his lifelong friend, the new pope, Urban VIII. However, in 1632 Galileo pushed his luck with the new pope to the limit by publishing Dialogue on the Two Chief World Systems. In this masterful (but satirical) work, Galileo had two people present scientific arguments to an intelligent third person, concerning the Ptolemaic and Copernican worldviews. The Copernican cleverly won these lengthy

This is a scaled, composite image (scale factor: each pixel equals 9.3 miles [15 km]) of the major members of the Jovian system—collected by NASA's Galileo spacecraft during various flyby encounters in 1996 and 1997. Included in the interesting family portrait is the edge of Jupiter with its Great Red Spot, as well as Jupiter's four largest moons, called the Galilean satellites. From top to bottom, the moons shown are lo, Europa, Ganymede, and Callisto. (NASA/JPL)

This is a scaled, composite image (scale factor: each pixel equals 9.3 miles [15 km]) of the major members of the Jovian system—collected by NASA's Galileo spacecraft during various flyby encounters in 1996 and 1997. Included in the interesting family portrait is the edge of Jupiter with its Great Red Spot, as well as Jupiter's four largest moons, called the Galilean satellites. From top to bottom, the moons shown are lo, Europa, Ganymede, and Callisto. (NASA/JPL)

arguments. Galileo represented the Ptolemaic system with an ineffective character that he called Simplicio.

For a variety of reasons, Pope Urban VIII regarded Simplicio as an insulting, personal caricature. Within months after the book's publication, the Inquisition summoned Galileo to Rome. Under threat of execution, the aging Italian scientist publicly retracted his support for the Coperni-can model on June 22, 1633. The Inquisition then sentenced him to life in prison, a term that he actually served under house arrest at his villa in Arceti (near Florence). Church authorities also banned the book Dialogue, but Galileo's supporters smuggled copies out of Italy, and the Copernican message continued to spread across Europe.

While under house arrest, Galileo worked on a less controversial area of physics. He published Discourses and Mathematical Demonstrations Relating to Two New Sciences in 1638. In this seminal work, he avoided astronomy and summarized the science of mechanics—including the very important topics of uniform acceleration, free fall, and projectile motion.

Through Galileo's pioneering work and personal sacrifice, the Scientific Revolution ultimately prevailed over misguided adherence to centuries of Aristotelian philosophy. Galileo never really opposed the church or its religious teachings. He did, however, come out strongly in favor of the freedom of scientific inquiry. Blindness struck the brilliant scientist in 1638. He died while imprisoned at home on January 8, 1642. Three-and-a-half centuries later, on October 31, 1992, Pope John Paul II formally retracted the sentence of heresy passed on him by the Inquisition.

Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment