Day 2: Pre Newtonian Universe

Time in History:

19 February 1473 - 8 January 1642
From the Birth of Copernicus to the death of Galileo

Key Concepts

Question of the Day: How many stars are visible from earth without a telescope?

What is the geocentric model of the universe?


Kepler - "As soon as somebody demonstrates the art of flying, settlers from our species of man will not be lacking [on the moon and Jupiter]... Given ships or sails adapted to the breezes of heaven, there will be those who will not shrink from even that vast expanse." Johannes Kepler, letter to Galileo, 1610

Lesson of the Day

The lesson today is framed by the work of three remarkable men; Nicolaus Copernicus (1473 –1543), Johannes Kepler (1571 –1630) and Galileo Galilei (1564 –1642). Prior to the contribution of these three individuals the earth was that to be positioned at the center of the universe. The work of these astronomers set the stage for Isaac Newton’s work including his theory of universal gravitation.

The geocentric model, also known as the Ptolemaic system, is a theory that was developed by philosophers in Ancient Greece and was named after the philosopher Claudius Ptolemy (circa 90 to 168 A.D.) It suggested that the planets, the sun, and even the stars orbited around the Earth. The geocentric theory had existed before Ptolemy; the model is described in early Greek manuscripts. As early as the 4th century B.C. Plato and Aristotle referred to a geocentric model of the universe.

As we learned on day 1, Ptolemy believed that each heavenly body was attached to its own sphere forming a set of nested spheres holding all celestial bodies seen from Earth. Although a complex explanation for the structure of the universe, the geocentric model survived well into the 16th century.

Nicolaus Copernicus was a Polish mathematician and astronomer who first suggested that the Sun, rather than the Earth sat at the center of the solar system. This model is called the heliocentric model of the solar system. Copernicus spent much of his adult life working on his theory of planetary motion, yet was reluctant to publish his theory as he was worried about possible scorn from the Catholic Church to which he belonged. He ultimately published his definitive work De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres), at the age of 70, shortly before his death. In Copernicus’ age his theory was not well regarded by many, including Martin Luther who wrote:

“People gave ear to an upstart astrologer who strove to show that the earth revolves, not the heavens or the firmament, the sun and the moon ... This fool wishes to reverse the entire science of astronomy; but sacred Scripture tells us [Joshua 10:13] that Joshua commanded the sun to stand still, and not the earth”

Twenty-eight years after Copernicus’ death, Johannes Kepler a mathematician and astronomer who was born in Germany. He was an enthusiastic supporter of the Copernican heliocentric theory. Kepler lived in a time when there was no clear division between astronomy and astrology, and occupied himself with many investigations that today would not be considered terribly scientific; he used many religious arguments to justify his theories. A brilliant mathematician and he believed that his mathematical formulations of planetary motion confirmed God’s design of the universe. Today Kepler is best known today for developing sophisticated mathematical formulae to describe the motions of the planets. Although filled with theological discourse Kepler’s work Mysterium Cosmographicum (The Cosmographic Mystery), proved an important step in modernizing Copernicus’ Heliocentric theory, and putting ‘mathematical bones’ to the motion of the planets.

The geocentric model that placed the Earth was at the center of the universe remained the broadly accepted theory for a century after the death of Copernicus. It was only the efforts of Galileo Galilei that finally served to convince most educated people that the Sun, not the Earth sat at the center of the solar system. Galileo has been called the father of modern observational astronomy, and it was his observations of Jupiter and Venus that convinced the great majority of astronomers that a heliocentric planetary model reflected the true structure of the solar system.

Firstly Galileo discovered the four moons and Jupiter and was able to observe that they orbited Jupiter. This finding contradicted the Geo-centric model that stated that all celestial bodies had to orbit the Earth. Secondly Galileo was able to observe a full set of phases – similar to those of the moon - of the planet Venus. Copernicus had predicted that planets orbiting the sun would exhibit all phases as it orbited the sun, as apposed to the Ptolemeic geo-centric model which predicted that planets would demonstrate only one at most two phases as they circled the Earth with the Sun. With these two observations Galileo provided conclusive evidence for the heliocentric model of the solar system, completing the work started over a hundred years before by Nicholas Copernicus. The moons of Jupiter are now called the Galilean moons in honor of his findings.

School Activity:

Do one of Galileo's experiments in your classroom. To understand the relationship between gravitational forces and the mass of objects, the changes in speed and direction of objects, and the distance between objects.

A pendulum is any mass which swings back and forth on a rope, string, or chain. Pendulums can be found in old clocks and other machinery. A playground swing is a pendulum.

If you pull the mass away from its rest position, so that the string is at an angle, and then let go, the mass will begin to swing back and forth. The length of time it takes the mass to swing all the way over and back, once, is called the period of the pendulum.

All three experiments will examine things we can do to the pendulum that will change the period. Here are the three questions we are asking:

  1. Does the amount of mass on the end of the string affect the period?
  2. Does the angle you pull pack the string to affect the period?
  3. Does the length of the string affect the period?

In these experiments, the dependent variable will always be the time for one full swing, or the period.

The three tested independent variables will be the mass, the angle, and the length of string.

The controlled variables will be the attachment point of the string, the string itself, the method used to time the pendulum, and the variables we are not currently testing. These will remain the same for each test, so that we know they won't affect the results.

Youth Ambassador Activity:

The Youth Ambassadors will build an orrery to demonstrate the arrangement and motion of planets.

An orrery is a mechanical model of the solar system device that illustrates the relative sizes, positions, and motions of the planets and moons according to the heliocentric model.


Origin Story of the Day:

Story of the Creation of the Universe - Ancient Greece

In the beginning, according to Hesiod, the universe was a shapeless mass called Chaos, which contained the seeds of all things in jumbled confusion. From Chaos sprang Erebos, the darkness that is under Earth, and divine Night. Next, Mother Earth came into being and Eros, love, who should rule the hearts of gods and men. Out of mother Earth came first the starry vault of Heaven, to be the abode of the gods, and the mountains and plans and waters that were to be the home of men and the lower animals. Now Love begins to stir among created things and brings together such as have a natural affinity; and thus from Chaos and Old Night are born Light and Day, and from Heaven and Earth are born the Titans, and hundred-handed monsters, and Cyclopes.

But these monsters filled their father Ouranos with fear, and to save himself from their attack he thrust them down to Tartarus, an abysm under the earth, where they lay until their mother Gaia took pity on them. By her Cronus, one of the Titans, was armed with a scythe and lay in wait for his father. Rushing out upon him he mutilated him with this horrible weapon and drove him from the field. From the blood of Uranus's wound that fell upon the land sprang the Giants and dread Furies, whose heads were wreathed with serpents, and from the blood that fell into the sea in his flight sprang Aphrodite.

So Cronus reigned in his father's stead and took to wife his sister Rhea. For ages they ruled over the universe, with the help of the other Titans, and to them were born in succession three daughters - Hestia, Demeter, and Hera, and three sons - Pluto, Poseidon, and Zeus. But the possession of children brought no happiness to Cronus for his father Uranus ha prophesied at that time of his mutilation that the children of Cronus would prove as undutiful to their father as Cronus had been to him; so he swallowed them one by one as they were born, until Rhea saved her sixth child by giving to Cronus in its place a stone wrapped in swaddling clothes. This he swallowed in all simplicity, while the living child was conveyed to Crete, where he was tended by the nymphs Adrastea and Ida, and nourished on the milk of the goat Amalthea. The cries of the young child were drowned by the Corybantes, the proof Rhea, as they sang their wild songs and clashed their weapons. In due course the child grew up to maturity and, aided by the counsels of Rhea and Gaia, proceeded to take vengeance on his father. A potion was administered to Cronus which compelled him to disgorge his cannibal repasts. First came up the famous stone, then the five brothers and sisters, all eager to avenge themselves on their unnatural father.

Character of the Day:

The Kepler Spacecraft is a space observatory launched by NASA to discover Earth-like planets orbiting other stars. The spacecraft, named after the Renaissance astronomer Johannes Kepler, was launched on March 7, 2009. As of February 2014, the Kepler spacecraft and its follow-up observations has detected 961 confirmed planets, including hot Jupiters, super-Earths, circumbinary planets, and planets located in the circumstellar habitable zones of their host stars. In November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy. 11 billion of these estimated planets may be orbiting sun-like stars.

As the Greeks noticed discrepancies between the way planets moved and the basic geocentric model, they began adjusting the model and creating variations on the original. In these models, planets and other celestial bodies move in circles that have been superimposed onto circular orbits around the Earth.