Directions: Read each slide

and decide what information is

needed. Some slides may have redor yellow or orange

underlined. This information is a

clue for you to read more

carefully or copy the information on your organizer!

The Geocentric Theory vs. The Heliocentric Theory

The Geocentric Theory

•The earth is located at the center of the universe and all the planets revolve around the earth.

Geocentric Cont…..•The Geocentric theory was believed by

the Catholic church especially because the

church taught that God put earth as the center of the universe which made earth special and powerful.

• The idea of the Earth actually moving was widely felt as a foolish suggestion because, as they saw it, if the Earth was

moving they would be able to feel it.Suffix: cen·tric :ADJECTIVE in or at the

center; central.

Proposed byAristotle (384-322 B.C.)

• Developed an early model based on the concept of uniform circularmotion. He placed the earth at the center of the universe and all of the planets, sun and stars around it.

• When Aristotle lived, if a person could “reason” out why something happened, then you didn’t need to do any experiments to see what would happen.

• This simple model of the revolutions of spheres could not explain all astronomical phenomena. In particular, planets were observed to wanderacross the fixed fields of stars over time; mostly they wandered in one direction, but occasionally they seemed to reverse course.

• To explain this strange retrogradation, Aristotle claimed that planets were attached, not directly to deferents, but to smaller spheres called epicycles. The epicycles were themselves attached to the deferents; the simultaneous revolution of both sets of spheres created an occasional apparent reversal of the planets' motions across the skies of the Earth.

• While Earth was enclosed by the celestial bodies spheres, the spheres actually revolved around a point called an eccentric, which was near the Earth but not quite on it.

• This elaborate theoretical system stemmed largely from two deeply held Greek beliefs: that the Earth was the center of the universe, and that all heavenly objects (celestrial bodies ) move in a uniform circular motion.

• In the realm of change, the natural motion of earthy materials was to seek the center of the universe.

• This is why Aristotle placed the earth at the center of the cosmos. This is also his explanation for why objects fall when dropped. A dropped object is just following its natural tendency to seek the center of the universe.

• Aristotle reasoned that if the earth rotated about its axis, we should fly off into space. Since we don't, the earth must be stationary.

• It would be almost 1900 years before Galileo introduced the concepts of gravity and inertia that explain why these effects are not observed even though the earth does move.

Supporter of GeocentricPtolemy (140 A.D.)

• Ptolemy advanced the geocentric theory in a form that prevailed for 1400 years.

• He added mathematics to support the theory

Ptolemy’s Problem

• Many supporters of the geocentric theory had one piece of evidence they couldn’t explain – the movement of MARS.

• Let’s take a break and investigate this movement.

Mars’ Motion

http://csep10.phys.utk.edu/astr161/lect/retrograde/retrograde.html

How did Ptolemy Explain this Problem?

• Ptolemy used geometric models to predict the positions of the sun, moon, and planets, using combinations of circular motion known as epicycles.

• An epicycle is an orbit within an orbit

• Having set up this model, Ptolemy then went on to describe the mathematics which he needed in the rest of the work.

Ptolemy’s Model –Epicycles Included

The Celestial Bodies: Geocentric

The Heliocentric Theory

• The word heliocentric comes from the Greek “helios,” meaning sun. Heliocentrism, an astronomical theory, assumes the sun is the center of the solar system and all planets orbit the sun. It did not fully emerge as a developed model until the late 16th century, with the work of Polish astronomer Nicolaus Copernicus.

• The Sun is the center of our solar system

Proposed byCopernicus (1473-1543)

• Polish astronomer who advanced the theory that the Earth and other planets revolve around the Sun. This was highly controversial at the time.

• The Ptolemaic model had been widely accepted in Europe for 1000 years when Copernicus proposed his model.

http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html

• Copernicus was told by many scholars that he should make his new findings accessible to others by publishing it. In 1543 the book called "On the revolutions of the heavenly bodies" was released. Copernicus's book had a great impact that angered the Catholic and Protestant Church.

• The Church became so angry – the Geocentric theory made human beings seem closer to God and since earth was in the center that meant humans were more special. The heliocentric theory changed that perspective completely, making humans lose that position in the universe.

Supports of Heliocentric Model

Other astronomers who made

further advances after Copernicus

were Johannes Kepler and

Galileo Galilei. For example, Kepler

showed that the planets do not orbit

in perfect circles, and Galileo built

very good telescopes that helped to

confirm the heliocentric model.

SupportersGalileo (1564-1642)

• An Italian scientist, Galileo was renowned for his contributions to physics, astronomy, and scientific philosophy. He is regarded as the chief founder of modern science.

• Galileo was condemned by the Catholic Church for his view of the cosmos based on the theory of Copernicus.

Galileo’s Books• Galileo published his discoveries and support

for the Copernican model in two books published in 1616 and 1632.

• Galileo was unusual for the time because he wrote in Italian rather than Latin like most scholars.

• Galileo also took great pains to make his books interesting often writing them in the form of dialogues rather than dry, boring dissertations.

• After his first book, "Starry Messenger", was published he was warned by the Church not to publicly support Copernicism again.

Heliocentric Evidence (Proof)/ CharacteristicsThis changed the way of thinking about the universe and differed from the religious beliefs at that time. The major feature of the Copernican theory can be summarized as follows:

1. The motion of the celestial bodies is uniform, eternal, and circular or compounded of several circles. 2. The center of the cosmos is the Sun. 3. Around the Sun, in the order of Mercury, Venus, Earth and Moon, Mars, Jupiter, and Saturn moves in their own orbits and the stars are fixed in the sky. 4. The earth has three motions; daily rotation, annual revolution, and annual tilting off its axis. 5. The retrograde motion or the backward motion of the planets is as explained by the Earth’s motion. 6. The distance from the Earth to the Sun is small compared to the distance to the stars.

Trial Before the Inquisition

• Galileo abided by this edict until 1632 when he published "A Dialogue on the Two Chief World Systems". This book's outright support for the Copernican model and its ridiculing of the Ptolemaic model earned Galileo a trial before the Inquisition.

• Galileo was accused of heresy and sentenced to house arrest for life. However, he got off easily compared to fellow Italian Giordano Bruno who was burned at the stake in 1600 for teaching Copernican ideas.

• In 1992, the Roman Catholic Church finally repealed the ruling of the Inquisition against Galileo. The Church gave a pardon to Galileo and admitted that the heliocentric theory was correct. This pardon came 350 years after Galileo's death.

Celestial Bodies (Objects)

Heliocentric versus GeocentricSimilarities / Differences

Heliocentric versus Geocentric: what is the difference between the two models? • In the geocentric model, the earth is considered as the center of the universe, and all celestial bodies move around the earth (planets, moon, sun and the stars). • In the heliocentric model, the sun is considered as the center of the universe, and the celestial bodies move around the sun.

(During the course of development of astronomy, many theories of geocentric universe and heliocentric universe were developed, and they have significant differences, especially regarding the orbits, but the core principles are as described above.)

What we know today!

Alike / Different