earth is the center of the universe. ancient societies were obsessed with the idea that god placed humans at the center of the universe.

the apparent change in the movement of the planet through the sky

supported and believed all of aristotle that matter is made of four elements: fire, water, earth and air and in additional aether (cosmos).

according to him, the earth was a sphere and the stationary center of the universe. the stars and planets were carried around the earth on spheres or circles, arranged in the order of distance from the center. these were the moon, the sun, venus, mercury, mars, jupiter, saturn, and the fixed stars.

(400 BCE - 355 BCE) he was considered as the first astronomer to explain the retrograde motion of the planets in the sky.

he found out the differences in the motion of each planet that should be considered to give an accurate description of the universe.

according to eudoxus’ model, the universe was composed of earth, five other planets (that are visible with the unaided eye, namely

eudoxus’ model eudoxus of cnidus (born c. 395 - 390 BC)

a greek astronomer and mathematician, was the first to propose a model of the universe based on geometry.

aristotle’s model aristotle (born c. 384 BC)

a greek philosopher and astronomer, considered the model proposed by eudoxus, considered these spheres as physical entities. he thought that these spheres were field with the divine and eternal “ether” that cause the spheres to move.

he introduced the prime mover, as the cause of the movement of the spheres.

keeps the stars moving in a constant motion, causing a friction to the smaller spheres of the outer planets and the spheres where the sun and the inner planets were located.

he believed so because earth is too big to move; thus it could not rotate. other celestial bodies were built up symmetrically in concentric spherical rings around the earth.

319 BCE - 230 BCE he was a greek astronomer who made the first attempt to create a heliocentric model of universe, which places the sun and the fixed stars were at rest, while earth revolved around the sun in a circular path.

arustarchus made the first attempt to create a ____________ model of universe, which places the sun and the fixed stars were at rest, while earth revolved around the sun in a circular path.

ptolemaic universe

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

he assumed that planets revolved on epicycles (small spheres) which moved around the deferent (large sphere).

ptolemy assumed that planets revolved on _________ (small spheres) which moved around the _________ (large sphere).

his model was considered more refined than previous geocentric models because his model could explain the motion of the celestial bodies accurately.

the center of the deferent is called the _________

what ptolemy did next was to “____” earth from its original position to a opposition below the center of the system that is still inside the deferent.

(1473-1543) during the 16th century, a polish astronomer, revived the heliocentric model of aristarchus.

he was hesitant to publish his findings because he was afraid of condemnation. but it was published a year before his death.

he strongly believed in the heliocentric model because there were loopholes in the ptolemaic model in terms of predicting the positions of the planets.

in copernicus’s model shown above, it could be concluded that:

(1546-1601) he was a danish astronomer who also made planetary observations.

unlike copernicus, he believed in a geocentric universe, but his idea of the geocentric universe is slightly different from ptolemy’s

in his model of the universe, called the “tychomic system”, earth was at the center and the sun and the moon revolved around it, and all the other planets orbited the sun. such a model was a type of “geoheliocentric system”

in brahe’s model of the universe, called the “________ ______”, earth was at the center and the sun and the moon revolved around it, and all the other planets orbited the sun. such a model was a type of “geoheliocentric system

in his model of the universe, called the “tychomic system”, earth was at the center and the sun and the moon revolved around it, and all the other planets orbited the sun. such a model was a type of “_______________ ______”