Origin of Modern
Astronomy
Key Terms
1. Astronomy – It is the science that studies the universe.
It includes the observation and interpretation of celestial
(spatial) bodies and phenomena.
2. Geocentric Theory - Earth centric Universe
3.Heliocentric Theory – Sun centric Universe
4. Gravity - the force that attracts a body toward the center
of the earth, or toward any other physical body having mass.
5. Inertia – The tendency of an object to resist a change
in motion.
6. Observatory – A building that contains one or more
telescopes.
Geocentric Theory
Ancient Greece
Geocentric Model: Ptolemy (87-150 AD)
Used epicycles to explain planetary movements
The Birth of Modern Astronomy
Copernicus - 1473-1543
 Suggested a model that the
Sun was the center of the
universe.
 This model explained the
retrograde
motion
of
planets better than the
geocentric model.
Heliocentric Theory
The Birth of Modern Astronomy
Tycho Brahe
 Tycho Brahe
 Johannes Kepler
-
1546-1601
 the greatest of the pretelescope observers in
Europe.
His measurements about the ,
positions of Sun, Moon and
planets, especially of Mars,
were far more precise than any
made previously.
Johannes Kepler - 1609
• Kepler was an assistant to Tycho Brahe.
• He used Brahe’s observations to study the orbit of Mars
• Discovered three laws of planetary motion: predict with
accuracy the motions of the planets.
Galileo - 1564-1642
 first scientist to use a telescope to observe
the sky.
 observed the phases of Venus and the moons
of Jupiter. Both observations supported the
heliocentric model.
Sir Isaac Newton – 1642-1727
 English scientist
 explained
gravity as the
force that
holds planets in
orbit around
the Sun.
Gravity’s Influence on Orbits
Gravity
• Gravity is the force that
– holds us to the Earth
– causes a rock to fall towards the ground
– causes the Earth to go around the Sun
– causes the Sun to be pulled towards the
center of the Milky Way galaxy
• Gravity acts between any two objects
even if they are far apart.
– “action at a distance”
Modern Universe
Is the Sun the center of the Universe?
Final Question
• Final Question