1) Ancient civilizations like those in Egypt, England, and Mesopotamia developed an interest in astronomy and incorporated astronomical alignments and knowledge into structures like Stonehenge and the pyramids. 2) The Babylonians made significant early contributions to astronomy, including compiling star catalogs and dividing the sky and time into degrees, minutes, and seconds as we still use today. 3) Greek astronomers built upon earlier traditions, seeking to understand physical principles and developing early astronomical models to explain observations. Key figures included Ptolemy, Hipparchus, and Aristarchus.

1. Since the dawn of civilization, humans have struggled to
make sense of the complex motions of celestial objects,
and countless ancient monuments and artifacts reflect
their fascination.
BEGINNINGS OF
ASTRONOMY

2. THE BABYLONIAN TRADITION
• Stonehenge in England and the Pyramids
of Egypt, both dating from around 2500
BC, embody astronomically significant
alignments based on knowledge of the
skies,but the true birthplace of
astronomy was in the Middle East.

3. • Two baked clay tablets produced around
700 BC by the Babylonians of present-
day Iraq summarize information on the
motions of stars and planets.
• The list of stars and constellations known
to the Babylonians is clear evidence of a
long-standing tradition of celestial
observation. Some constellations, such as
Leo and scorpius, have come down to us
virtually unchanged.
THE BABYLONIAN TRADITION

4. THE BABYLONIAN TRADITION
• the Babylonians made another lasting
contribution to astronomy: having measured the
length of the year as approximately 360 days,
they divided the circle of the sky into 360
degrees, subdivided each degree into 60 parts,
and introduced the 24-hour day, with each hour
also divided into 60 parts.

5. GREEK ASTRONOMY
• the Greeks sought to understand
the physical principles on which the
universe worked, thus initiating the
separation of science from
superstition.

6. • Eudoxus
• 4th century BC, developed Celestial Model
•a scheme of 27 crystalline spheres all
nested within each other, rotating on
different axes and at different speeds, which
carried the celestial bodies around the
spherical Earth.

7. • Hipparchus
• compiled the first accurate catalog of the
naked-eye stars in the 2nd century BC.
• classified stars into six categories of
brightness

8. • Ptolemy (second century AD)
• presented a summary of Greek astronomical knowledge
in a work usually known as the Almagest, meaning
―greatest,‖ a name given to it by later Arabic astronomers.
• This included an updated version of Hipparchus’s
catalog, expanded from 850 stars to over 1,000 and
arranged into 48 constellations— the foundation of our
present-day constellation system.

9. • Ptolemaic
Model

10. ARABIC ASTRONOMY
• al-Sufi (before 1000 AD)
• produced a revised version of Ptolemy’s
star catalog, called the Book of the
Fixed Stars.
• Also contained drawings of each
constellation.

11. THE REBIRTH OF WESTERN ASTRONOMY
• Nicolaus Copernicus (1473–1543)
• revived the sun-centered or
heliocentric theory proposed by the
Greek philosopher Aristarchus in the
3rd century BC.

12. • Tycho Brahe (1546–1601), a Danish nobleman
• Between 1576 and 1586, he built two
observatories, called Uraniborg and
Stjerneborg, on the island of Hven, between
Denmark and Sweden
• Model: Earth remained stationary at the
center, orbited by the Moon and sun, while
the planets orbited the moving sun.

13. •Johannes Kepler (1571–
1630)
•discovered that the planets
do indeed orbit the sun

14. GALILEO’S DISCOVERIES
• greatest pioneer of telescopic astronomy
• Moon’s surface was not a smooth, polished sphere but was scarred by craters and
mountains
• Jupiter was orbited by four moons (Galilean satellites)
• Venus shows phases
• glimpsed the rings of saturn
• swept away the old Earth-centered view of the universe for good
• Acceleration due to gravity

15. NEWTON AND GRAVITY
• deduce his law of gravity, publishing
it in 1687 in Principia Mathematica.

16. • Edmond Halley (1656–1742)
• calculated that comets move around
the sun on highly elliptical orbits.
• Convinced that the comets seen in
1531, 1607, and 1682 were one and
the same, Halley predicted that the
comet would return around 1758