Galileo for Kids

His Life and Ideas

Chicago Review Press Incorporated

Contents

SCIENCE AND ASTRONOMY BEFORE GALILEO

The earliest astronomers were simply observant and curious people who happened to notice the movement of heavenly bodies. Many advanced civilizations made astronomical observations thousands of years ago and applied them to the creation of calendars. Different philosophers and scientists proposed various theories over the years. Some thought that the earth was flat. One Greek scientist thought the earth was a cylinder, another that the universe was shaped like an egg. Around 500 B.C. a philosopher and mathematician named Pythagoras (c. 580–c. 500 B.C.) believed that the sun was the center of the world, around which the earth moved.

Aristotle (384–322 B.C.) believed that the earth was round and was at the center of the universe. He believed that the sun and the planets revolved around the earth. Aristotle was the pupil of the philosopher Plato and was himself a philosopher and scientist whose works became the standard in universities across Europe for many hundreds of years after his death. Topics he wrote about included logic, physics (the science that deals with the physical properties of solids, liquids, and gases), and politics.

A great advance in science came around 200 B.C. when Eratosthenes of Cyrene figured out a way to calculate the size of the earth. He used the angle of the sun in the sky at two different places of a known distance apart — Alexandria and Syene (now know as Aswan) — to calculate the circumference of the earth (total distance all the way around the globe). An astronomer named Hipparchus catalogued more than 800 stars that he saw in the sky, and placed them into groups according to their brightness.

The next theory to be proposed was somewhat of a setback for astronomy. Claudius Ptolemy (c. a.d. 100–c. 170) was an Egyptian philosopher and scientist who lived in the great city of Alexandria. He lived at a time when the Romans ruled over Egypt. Ptolemy, the author of an encyclopedia on astronomy, agreed with Aristotle and thought that the unmoving earth was the center of the universe.

In Ptolemy's mind, everything else in the sky revolved around the earth from east to west every 24 hours. The planets and stars were set into hollow spheres around the earth. Each sphere contained different celestial objects: the first sphere closest to the earth contained the moon, the second sphere contained the planet Mercury, the third had Venus, the fourth had the sun, followed by the fifth, sixth, seventh, and eighth spheres for Mars, Jupiter, Saturn, and the fixed stars, respectively. The theory explained that the sun and moon not only appeared to move in the sky, but also in fact really were moving around the earth. This scheme of planetary motion became known as the Ptolemaic system.

The ancients saw all the stars in the sky and tried to make sense of what they saw. Mapping and organizing the stars was difficult until people came up with a way to simplify the process. Using the different stars as dots, they connected the points to make the foundation for "pictures" of animals, shapes, and mythological people. The signs of the zodiac are constellations, or groups of stars: Taurus (the Bull), Aries (the Ram), and Leo (the Lion). Other well-known constellations are Orion (the Great Hunter), Cassiopeia (the Queen of Ethiopia), and Ursa Major (the Greater Bear, also known as the Big Dipper).

During the fall of the Roman Empire in the fifth century a.d., barbarian tribes spread across Europe from the east. In Europe, for almost a thousand years, there was a period of limited innovation known as the medieval era, or the Middle Ages. The term "Dark Ages" has also been used but is probably too strong to describe this period. There were of course great artists and scientists during the Middle Ages, but not at the level of earlier times. Elsewhere in the world, however, science still progressed. On July 4 of the year a.d. 1054, Chinese astronomers observed a sudden "new" star in the sky — actually, it was the death of a star, today known as a supernova, or exploding star. The remains of this are known today as the Crab Nebula. This star was so bright it rivaled the moon, and it was even visible during the day for a few weeks.

It was not until about the year 1400 in Europe that creativity and exploration exploded again as it had during ancient Greek and Roman times. The Renaissance (French for "rebirth") that blossomed in 15th-century France, Italy, and Germany was a time for rediscovery of great cultural traditions that had first been introduced thousands of years before. The spirit of the Renaissance was that great minds were open to all subjects. Creativity and invention ruled. Great works of architecture, sculpture, and painting were created during the years 1400 to 1600, using the template of the Greek and Roman masterpieces from 2,000 years before.

EXPLORATION·AND·DISCOVERY DURING THE·RENAISSANCE

Italy, and especially the city of Florence, was one of the most active hotbeds of Renaissance activity, with the likes of the multitalented Michelangelo Buonarroti (1475–1564) and Leonardo da Vinci (1452–1519) working there. Leonardo was an artist and scientist, and he applied his special genius to anything he tried to do. Leonardo's curiosity led to detailed drawings of the various parts of the human body that showed organs and muscles, skin and bones. He was also interested in astronomy and tried to prove mathematically that the sun was larger than the earth.

The rebirth of scientific thought during the Renaissance ran a more bumpy course than did the rebirth of art. Christopher Columbus, Vasco da Gama, Sir Francis Drake, and Amerigo Vespucci were among the many who bravely set sail and explored the world by ship during this period. People still thought the earth was flat until Ferdinand Magellan's crew (Magellan himself had been killed partway through the journey) proved it was not flat by traveling around the globe in the year 1522. Exploration of the world led to discoveries of new continents and the colonization of distant lands.

The science of mapmaking (cartography) slowly blossomed as people realized the true shape of the earth's land masses and bodies of water. Sebastian Münster was a German cartographer who updated the maps of Ptolemy in 1540, and in 1544 published the first edition of his Cosmography, a geography of the world enhanced with images of historic events, scientific information, city views from around Europe, as well as the customs and legends of different peoples (see pages 12 and 20 for Münster illustrations). This popular work was reprinted in numerous later editions and translated into several languages. Unfortunately, before he could complete any other works, Münster died of the widespread disease known as the bubonic plague. Gerardus Mercator was another pioneer in map and globe making whose way of depicting the world, known as the Mercator Projection, was a lasting contribution. The Mercator Projection was a method devised for projecting the round globe onto a flat map.

During the Renaissance, more sophisticated navigational instruments helped sailors find their way across the oceans. Still, as late as the mid-1500s, the correct shapes of all the continents and the size of the Atlantic and Pacific oceans were not yet known.

New discoveries were also made in medical sciences: anatomy, biology, and chemistry. Even so, great deadly epidemics of the plague continued to erupt across the cities of Europe during the 1400s and 1500s.

The rebirth of ideas led to a rebirth of literature. All types of writing flourished during this time. Because travel across Europe was slow and difficult (especially across mountainous regions), scientists and great thinkers of the Renaissance communicated through letters. The art of letter writing blossomed, and, in this way, new and revolutionary ideas could be spread to all parts of Europe.

ASTRONOMY·DURING THE·RENAISSANCE

The Renaissance gave the world beautiful artwork and architecture based on the rebirth of the classical ideas of ancient Greek and Roman times. Unfortunately, astronomy was one place where the theories of classical times should have been abandoned. By 1500 the educated world still believed in the theories of Aristotle and Ptolemy and other ancient scientists and philosophers. During the 16th century, advances in astronomy slowly made headway toward an understanding of the true nature of the universe.

Those scientists who felt it important to make a careful study of the skies included a pair of Polish astronomers, Peter Apian and Nicolaus Copernicus.

PETER·APIAN

Peter Apian (1495–1552; born Peter Bienewitz) was a noted mapmaker and astronomer who in 1531 made careful observations about the comet (a traveling celestial body made up of ice and rock) later known as Halley's Comet. Apian also observed comets in 1532, 1533, 1538, and 1539. He noted that the tail of a comet seemed always to point away from the sun. In 1536 Apian published a fairly accurate woodcut illustration showing the location of 48 different constellations in the sky. Apian also created astronomical instruments and wrote a book called Astronomicum Caesareum (Astronomy for a King) in 1540. One of his other contributions was proposing a method of determining lines of longitude (imaginary north-south lines used for navigation) using the distance of the moon to the earth.

NICOLAUS·COPERNICUS

In 1530 a respected Polish monk and scientist named Mikolaj Kopernik, more commonly known by his Latin name, Nicolaus Copernicus (1473–1543), finished a book he had been working on for 20 years. It was titled De Revolutionibus oblure coelestium (The Revolution of the Celestial Orbs), and it completely opposed the Ptolemaic system. Copernicus was a university-educated man who had become a monk. He felt that publishing his book would be very risky because of how the Catholic Church might react to the new and strange idea that the earth was not the center of the universe. The Church's teachings said that the earth was the center of creation, and everything else in the universe operated in relation to it. Copernicus also knew that, though they had different opinions than the Catholics on many subjects, the followers of Martin Luther (1483–1546), who broke away from the Catholic Church to form what would become the Lutheran Church, might have the same negative reaction to his new theory.

Copernicus's work proposed that the earth revolves around its own axis (similar to the way a top spins), from west to east, every 24 hours, and that this was the reason the sun, moon, and planets appeared to move in the sky. Copernicus also believed that the sun was the centerpoint around which the earth and other planets revolved.

His friends, including a cardinal and a bishop, practically had to beg Copernicus to get the manuscript published. When he finally did agree to let his book be published in 1543, he tried to protect himself from any possible controversy by dedicating the book to Pope Paul III (1468–1549). By this time, Copernicus was old and very sickly. As he lay on his deathbed, he was brought a copy of the newly printed book.

It was perhaps for the better that the partly paralyzed and senile Copernicus could not see or read it. Editorial changes had been made by his friend Andreas Osiander, who was overseeing the publication of the book. The only problem was that Osiander was a minister, a former Catholic who had converted to the Lutheran faith and who did not believe the Copernican theory should be stated as fact. He had added the word "hypothesis" to the title page. (A hypothesis is defined as merely conjecture — an educated guess — whereas a theory is based more on factual observations.) He also replaced Copernicus's preface with entirely new text, which told readers that astronomy was not necessarily going to provide definitive answers.

Despite these drastic changes, the main body of the work was unchanged. Though seemingly opposed to the views of the Bible that the earth was the center of the universe and the heavens were unchanging, his work was virtually ignored by the Catholic Church, and none of the popes during the 16th century made any fuss over the book or its theories. Pope Paul III actually liked the book. Martin Luther and some of his followers, however, condemned the book, picking up on the contradictions that the Copernican theory had with some passages of the Bible.

ASTRONOMY·IN·THE·1570s: A·NEW·STAR?

Besides Copernicus, other Europeans made advances in astronomy during the 16th century. These included Philipp Apian (1531–1589) and Michael Maestlin (1550–1631). Apian, who was Maestlin's teacher at the University of Tübingen, was the son of the mapmaker Peter Apian.

In November 1572 a bright new object suddenly appeared in the constellation Cassiopeia. Astronomers, including Apian and Maestlin, made note of this. Was this object a comet? After all, comets were the only known objects that seemed to appear out of nowhere. But this "comet" was different. It had no tail, for one thing.

Maestlin, a Lutheran, realized that proposing new theories about the heavens could interfere with Lutheran Church ideas. But Maestlin found a way to justify his research of the planets, stars, and comets. He said that by studying the exact nature of these heavenly objects, we would be better able to understand God's design of the universe.

Whatever the truth was about the skies above, Maestlin wrote, it was created by God. In the end it did not matter whether the new truth was different from what we originally thought or not. Whatever we discover to be true, it must be God's truth. Accurate observation was the only path to truth, and was more important than defending old theories. In 1573 he published Demonstratio astronomica loci stella (Astronomical Explanation about Stars). In this work, he wrote that the object that had appeared in the sky was not a comet, and was too far away to be a planet, so it had to be a new star. According to Aristotle's view of the universe, the realm of the stars was supposed to be unchanging. The old teachings said that there was nothing new to be revealed in the skies, no new surprises or secrets. Aristotle believed that whatever was there, it would always be the same. But here was a new star suddenly appearing in the sky! Maestlin wrote in his work that the opinions of Aristotle and Ptolemy were wrong because they contradicted the observations he had made.

TYCHO·BRAHE

Another person who noted the new star of 1572 was a Danish astronomer named Tycho Brahe (1546–1601). Educated at the University of Copenhagen, Brahe was inspired to take up the study of astronomy by a solar eclipse (an event that occurs when the moon passes in front of the sun) he saw in 1560. An evening duel in December 1566 cost Brahe part of his nose, which he replaced with a gold copy. This did not prevent him from furthering his career, and he designed astronomical instruments including a huge quadrant (an instrument to find the altitude, or height in the sky, of a celestial object) that took many men to construct.

On the night of November 11, 1572, Brahe happened to be studying the sky when he noticed a bright star with which he was unfamiliar. He quickly asked around to see if anyone else had noticed this new star. Brahe made measurements of the location, brightness, and color of the star and followed it over the 16 months that it lit up the night sky. He noticed that the twinkling light grew in intensity over the months of early 1573, until it was brighter than even the star called Sirius and larger than the planet Jupiter. He watched it change from a strong white to yellow to red to blue and then become pale and finally fade away in early 1574. At the urging of a friend, he published his findings in a book.

As we now know, what Brahe and others witnessed was really a super-nova. Supernovae are rare events — the last one visible from earth happened in 1604.