This document discusses ancient astronomy from several prominent ancient Greek astronomers and their findings and theories. It mentions that the Greeks noticed the North Star was closer to the horizon in Egypt compared to Greece. It also discusses Aristotle arguing the Moon and Sun must be spherical if they cause eclipses. Eratosthenes accurately calculated the circumference of Earth to be approximately 40,000 km by comparing shadows at different locations. Ptolemy later believed the Earth was the center of the universe in his Ptolemaic model of celestial spheres.

1. Ancient
Astronomy

2. ANCIENT
ASTRONOMY

3. ANCIENT
ASTRONOMY

4. ANCIENT
ASTRONOMY

5. ANCIENT
ASTRONOMY

6. ANCIENT
ASTRONOMY

7. ANCIENT
ASTRONOMY

8. ANCIENT
ASTRONOMY

9. ANCIENT
ASTRONOMY

11. ANCIENT
ASTRONOMY
NORTH STAR
-was believed to be at fixed
position in the sky, however
when the Greeks traveled to
places nearer the equator, like
Egypt, they noticed that it is
closer to the horizon

12. ANCIENT
ASTRONOMY
Aristotle argued that if the
Moon and the Sun were both
spherical, then perhaps the
Earth was the same

13. ANCIENT
ASTRONOMY
Disappearing ships
- If the Earth was flat, then a
ship traveling away from an
observer should become
smaller until it disappeared..
But the Greeks observed that
the ship became smaller and
its hull disappeared first
before the sail.

14. Size of the
spherical Earth
ERATOSTHENES – gave
the most accurate size
during their time.
Syene (Southern Egypt)
and Alexandria : Vertical
object shadow
From his measurement: he
computed the
circumference of the Earth
to be approx. 250,000
stadia, about 40,000 km

15. ANAXAGORAS
ANAXAGORAS – was able to
explain what causes the
phases of the moon. To him,
the moon shone only by
reflected sunlight. Since it is a
sphere, only half of it
illuminated at a time and it
changes periodically.

16. Eudoxus
EUDOXUS – proposed a
system of fixed spheres. He
believed that the sun, moon
and the five known planets
and the stars were attached to
these spheres which carried
the heavenly bodies while they
revolved around the stationary
Earth.

17. ARISTOTLE
ARISTOTLE – was a student of
Plato. For him, the earth is
spherical in shape since it
always casts a curved shadow
when it eclipses the moon.
He also believed that the Earth
was the center of the universe

18. ARISTARCHUS
ARISTARCHUS – very first
Greek to profess the
heliocentric views
“helio” – sun
“centric”- centered

19. Eratosthenes
ERATOSTHENES – the first
successful attempt to
determine the size of the Earth
was made by him by applying
geometric principles.
-he observed that at the
noonday sun in two Egyptian
cities that were almost
opposite each other – Syene
(Aswan) in South and
Alexandria in the North. He
assumed they were in the same
longitude.

20. Hipparchus
HIPPARCHUS – is considered as
the greatest of the early Greek
astronomers who compared and
observed the brightness of the
850 stars and arranged them into
order of brightness or
magnitude.
-he also developed a method for
predicting the times of lunar
eclipses to within a few hours.
-he also measure the length of
the year to within the minutes of

21. CLAUDIUS
PTOLEMY
CLAUDIUS PTOLEMY – believed
that the Earth was the center of
the universe.
His Ptolemic model claimed the
planets moved in a complicated
system of circles

23. PTOLEMIC
MODEL
The sun, moon and other planets
move in circular orbits around
the Earth. However, if observed
night after night, these planets
move slightly eastward among
the stars.
RETROGRADE MOTION –
planets moves in the opposite
direction for some time, after
which it resume its eastward
motion

24. ARISTOTLE’S
CONCLUSION
He lived in ancient Greece more than
300 yrs before the common era (BC).
In those days, most people believed
that many gods ruled the universe.
He is regarded as the Father of
Natural Science. His methods were
basis for scientific method.
He considered the position of the
North Star
He also observed that he could see
the top of the sails first before the
rest of the ship. (because of the

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