Different Models of the Universe

Before the telescope was invented, ancient astronomers only used their unaided eyes to observe the sky and the stars. Eventually, they created models of the universe. Here are some astronomers who constructed their own models of the universe. 

Geocentric Model- Believed that Earth was at the center of the universe. Here are some models that are geocentric model.

1. Eudoxus of Cnidus

(Eudoxus's geocentric model of the universe:

 Earth surrounded by concentric spheres)

According to Eudoxus's Model, the universe was composed of Earth, five other planets that are visible with the unaided eye (Mercury, Venus, Mars, Jupiter, and Saturn), sun, moon and motionless stars which were enclosed in spheres. Earth was motionless at the center of the universe. Each of the five other planets was enclosed in four concentric circles. The sun and moon were each enclosed in three concentric spheres. Lastly, the group of motionless stars lay in the outermost sphere. 

FACT:

Eudoxus was a Greek philosopher, astronomer,and mathematician. He was considered the first astronomer to explain the retrograde motion of the planets in the sky.

2. Aristotle

(Aristotle's model of the universe)

Aristotle's model showed that the universe was spherical and finite. Just like Eudoxus, he perceived Earth was at he center of the universe and was stationary. He believed so because Earth is too big to move; it could not move.

He believed that Earth was composed of four elements- earth, water, air, and fire. He further described that each ring was in physical contact with one another.

FACT:

Aristotle was a Greek philosopher who wrote about many subjects and made a number of important contributions to science based ones such as physics, biology, anatomy, geology and zoology. 

3. Claudius Ptolemaeus (Ptolemy)

(Ptolemy's model of the universe)

In his model, it is assumed that Earth was at the center of the universe, while the other celestial bodies revolved around Earth in perfect circles with constant velocity.

(A closer look at Ptolemaic's model of the universe)

Ptolemy assumed that the planets revolved on epicycles (small spheres) which move around the deferent (larger spheres).The center of the deferent is called the eccentic. Ptolemy did next was to "move Earth from its original position to a position below the center of the system that is still inside the deferent. 

4. Tycho BraheIn Brahe's model of the universe, called the Tychonic system, Earth was at the center and the sun and the moon around it, and all the other planets orbited the sun. 

Fact:
Tycho Brahe was a Danish astronomer who also made planetary observations. He observed the sky night after night using the most accurate instruments he could find.








Heliocentric Model- Believed that the sun was at the center of the universe. Here are some models that are heliocentric model.

1. Aristarchus of Samos

Aristarchus proposed that the sun and the fixed stars were at rest, while earth revolved around the sun in a circular path.

He wrote a book entitled On the Sizes and Distances of the Sun and the Moon. In this book, Aristarchus calculated the distances from Earth by estimating the relative angles of the moon and the sun from Earth. He had 3 assumptions:(a)Earth was spherical (b)It is far from the sun (c)Moon passes through the Earth's shadow when they align.


FACT:

Aristarchus was a Greek astronomer who made the first attempt to create a heliocentric model.

2. Nicolaus Copernicus

Copernicus strongly believed in the heliocentric model because there were loopholes in the Ptolemic model in nterms of predicting the positions of the planets. In Copernicus's model, it could be concluded that (a)heavenly bodies exhibited constant circular and perpetual motion along their epicycles, (b) the sun was at the center of the universe, and (c) the order of the planets from the sun is Mercury, Venus, Earth (and moon), Mars, Jupiter, Saturn, and beyond the planets were the fixed stars.
FACT:Copernicus, a Polish astronomer, revived the heliocentric model of Aristarchus. He was hesitant to publish his findings because he was afraid of condemnation. It took him long time to publish his work. His works were published a year ago before his death.