Scientists who had an early concept about the universe

1. Models Of The
Universe

3. Eudoxus Of Cnidus
 One of the best mathematicians
and astronomers of the Plato era,
EUDOXUS OF CNIDUS around
400 B.C devised the system o
concentric spheres and gave the
first systematic explanation of
the movements of the sun, the
moon and the planets,
emphasizing once again the
ancient Greek’s insistence in the
spherical perfection .

5. Aristotle  Aristotle somehow patterned his model
to the model of Eudoxus. Aristotle’s
model of showed that the universe was
spherical and finite. Just like Eudoxus,
he perceived Earth was at the center of
the universe and was stationary. He
believed so because Earth is too big to
move; thus, it could not rotate.
 Aristotle believed that Earth was
composed of four elements; Earth,
Water,Air and Fire.
TAKE NOTE: Both models of
Eudoxus and Aristotle were
considered Geocentric. This means
that both astronomers believed that
Earth was at the center of the
universe.

7. Aristarchus
Aristarchus (BCE-230 BCE) was a Greek
astronomer who made the first attempt to
create a Heliocentric Model, which places
the sun at the center of the Universe. He
proposed that the sun and the fixed stars
were at rest, while Earth revolve around the
sun in a circular path.

9. The only work of Aristarchus that survived was entitled On The Sizes And
Distances Of The Sun And The Moon. In this book, Aristarchus calculated the
sizes of the sun and the moon and their distances from Earth by estimating
the relative angles of the moon and the sun from the Earth.
He had three assumptions
a) Earth was Spherical
b) It is far from the sun
c) Moon passes through Earth’s shadows when they align

10. Claudius Ptolemaeus (Ptolemy)
In this 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. Ptolemy’s model was considered
more refined than the previous Geocentric models
because his model could explain the motion of the
celestial bodies accurately.
Ptolemaic Universe

11. Ptolemy (100-AD-178 AD)
assumed that the planets revolve
on epicycles (small spheres) which
moved around the deferent (large
sphere). He added that the stars
belonged to the celestial sphere
which was located beyond the
planetary spheres.

12. The center of the
deferent is called the
eccentric. What
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.

13. Nicolaus Copernicus
During the 16th Century, Copernicus (1473-1543), a polish
astronomer, received the heliocentric model of Aristarchus. He
was afraid of condemnation. Because of this, it took him a long
time to publish his work. His works were only published a year
before his death.
Copernicus strongly believed in the heliocentric model because
there were loopholes in the Ptolemaic model in terms of
predicting the positions of the planets.
a. Heavenly bodies exhibited constant circular and perpetual motion
along their epicycles
b. The sun was at the center of the universe
c. The order of the planets from the sun is Mercury, Venus, Earth (and
moon) Mars, Venus, Saturn and beyond the planets were the fixed
stars.

15. Tycho Brahe
Tycho Brahe (1546-1601) was a
Danish astronomer who also
made planetary observation.
Unlike Copernicus, Brahe believed
in a geocentric universe, but his
idea of the geocentric universe is
slightly different from Ptolemy’s.

16. In Brahe’s model of the universe, called the Tychonic System, earth
was at the center and the sun and the moon revolve around it, and
all the other planets orbited the sun. Such a model was a type of the
geoheliocentric system.