1) Ancient Greek thinkers like Pythagoras, Anaxagoras, and Aristotle provided evidence that the Earth was round rather than flat based on observations of lunar eclipses, the positions of stars, and ships disappearing over the horizon. 2) Eratosthenes directly measured the circumference of the Earth in the 3rd century BCE by comparing the angles of shadows cast by sticks in Alexandria and Syene on the summer solstice, determining that the Earth must be spherical. 3) The ancient Greeks developed models of celestial motion including diurnal motion of the stars, annual motion of the sun, and precession of Earth's axis to explain their observations of the heavens.

1. HOW WE CAME
TO REALIZE
THAT EARTH IS
NOT THE
CENTER OF THE
UNIVERSE?
Prepared by: Miss Charry Cervantes

2. GREEK VIEWS
OF MATTER
AND MOTION
Your Name
Class Name

3. They believed that objects were
made up of four elements: air, earth,
fire, and water.
They supposed that there were
different types of motion that caused
stationary objects to move and
moving objects to stop.

4. OF MOTION
ACCORDING
TO
ARISTOTELIA
N
MECHANICS

5.  Natural
 Voluntary
 Involuntary

6. Natural motion
 the tendency of objects to go back
to their natural state
 For example, the natural motion of
a rock, which is made up of the
element earth, is to go downward or
toward the ground. This notion
explained why a stone that was
thrown upward always fell back to

7. Voluntary motion
 the ability of humans (as well as
other animals) to move because
they have the will or the capacity
to do so

8. Involuntary motion
 the motion caused by unnatural
conditions
 For example, a plant does not
have the ability to move around,
but it can be mechanically
moved by air or water.

9. NON-TERRESTRIAL
MOTION,
ACCORDING TO THE
ANCIENT GREEK
ASTRONOMERS
Your Name
Class Name

10. Diurnal motion
 refers to the apparent
movement of stars and other
celestial bodies around the
Earth. It is caused by Earth’s
rotation from west to east.

11. Diurnal motion

12. Annual motion
 refers to the apparent yearly
movement of the Sun across a
background of stars. This
movement is caused by Earth’s
revolution around the Sun.

13. Annual motion

14. Precession
 refers to the conical motion of
Earth’s axis as it spins. Because
of precession, Earth’s axis shifts
very slowly, completing one
cycle every 26 000 years.

15. Precession

16. SHAPE OF THE
EARTH…ROUND
? SPHERICAL?
PLANE OR DISK?
Your Name
Class Name

17. Around 500 BCE
 Pythagoras and his pupils
proposed that Earth was round

18. Anaxagoras (Around 430 BCE)
Conducted observations that
supported Pythagoras’s
proposal.
He observed that during a lunar
eclipse, the Earth’s shadow was
reflected on the moon’s surface.
The shadow was circular.

19. Aristotle (Around 340 BCE)
 Listed several arguments for a
spherical Earth, which included
the shape of the moon and the
sun, the positions of the North
Star, and the disappearance of
the ships when they sailed over
the horizon.

20. Aristotle (Around 340 BCE)
Aristotle argued that if the moon and the sun
were both spherical, then perhaps, Earth was
also spherical.
The North Star was believed to be at a fixed
position in the sky. However, when the Greeks
traveled to places nearer the equator, like
Egypt, they noticed that the North Star is closer
to the horizon. Aristotle argued that such an
observation is only possible if Earth was round.

21. Aristotle (Around 340 BCE)
If the Earth was flat, then a ship traveling
away from an observer should become
smaller and smaller until it disappeared.
However, the Greeks observed that when
the ship sailed, the hull disappeared first,
which implied that the surface of the
Earth was curved.

22. Eratosthenes (Around 240 BCE)
 Attempted to measure the circumference
of the Earth.
 He received correspondence from Syene
in Southern Egypt. It stated that a vertical
object did not cast any shadow at
noontime during the summer solstice.

23. Eratosthenes (Around 240 BCE)
 However, this was not the case in
Alexandria where, at noon time during the
summer solstice, a vertical object still cast
a shadow. These observations could only
mean that the Sun, during this time in
Alexandria, was not directly overhead.

24. Eratosthenes (Around 240 BCE)
 Eratosthenes determined the angle that
the Sun made with the vertical direction
by measuring the shadow that a vertical
stick cast. He found out that in Alexandria,
the Sun makes an angle of 7.2° from the
vertical, whereas in Syene, the Sun
makes an angle of 0°. To explain the
difference, he hypothesized that the light
rays coming from the Sun were parallel,

25. Eratosthenes (Around 240 BCE)
 From his measurements, Eratosthenes
computed the circumference of the Earth
to be approximately 250 000 stadia or 46
250 km (1 stadia = 185 m).

26. Eratosthenes (Around 240 BCE)