Download The History of Meteorology

The History of Astronomy ~ Chapters 4 & 5
Birth of Cosmological Models
• Babylonians
– 1600 B.C.: first star catalogs
compiled; recording of
planetary motion
– 800 B.C.: planetary locations
with respect to stars of zodiac
– 240 B.C.: observation of
eclipses
Birth of Cosmological Models
• Greeks ~600 B.C.
– geometrical, physical models
of cosmos – based on the
ideal of the sphere as the
perfect form
– Pythagoras used geometry to
develop a model of the cosmos
• a series of concentric
spheres centered around the
earth – GEOCENTRIC
Birth of Cosmological Models
• Greeks
– 427–347 B.C.
Plato –
heavenly bodies move at a
uniform rate
– 384-322 B.C.
Aristotle –
used 56 spheres and took into
account physical ideas of
motion: natural motion &
forced motion
Birth of Cosmological Models
• Greeks
– ~300 B.C.: Greek astronomer
Aristarchus proposed a
HELIOCENTRIC (suncentered) model of cosmos
– much of his writings were
lost; model attacked because
it contradicted Aristotle’s
physics
Birth of Cosmological Models
• Greeks
– ~A.D. 125 Ptolemy – first
astronomy textbook
• earth is spherical and at center
of cosmos & doesn’t move
• predicted planetary motion in a
GEOCENTRIC cosmos with
accuracy
• accepted for 1,400 years
Copernicun Revolution
• Copernicus proposed a
heliocentric universe
• Marked the birth of modern
science
• Long association with the
church
– Reluctant to publish ideas that
contradicted church teaching
Copernicun Revolution
• 1507 – started his writings
• Didn’t authorized publishing until
1543 – he was dying
• Hypothesis was correct – sun at
center of cosmos
• Model was inaccurate
– His belief in uniform circular motion
did not accurately explain the
motion of the planets
Galileo Galilei
• Concentrated more on terrestrial physics than
telescope observations
• Used telescope to give support to Copernican
model
• Refuted two Aristotelian ideas:
– Observations of moon geography dismissed the
idea of a perfectly spherical body
– Observations of Milky Way dismissed the idea of
a set number of stars
• Discovered four new “planets”
– really the moons of Jupiter, therefore, things
revolve around something other than the earth
Galileo
• His evidence didn’t actually
support the Copernican model,
but it provided evidence against
the Aristotelian-Ptolemaic
model
• Investigated and proposed
“new” properties of physics:
speed, velocity, acceleration,
inertia, free-fall due to gravity
Isaac Newton
• Provided laws of motion and gravity that apply on
earth and in the celestial realm (goes against
Aristotle)
• Discovered:
– laws of gravity that explain planetary motion.
– that the force of gravity varies depending on the inverse
square of the distance between two bodies.
– The strength of the gravitation force depends directly
on the product of the masses of the two objects and
inversely on the square of the distance between their
centers – this explains the elliptical orbits – supports
Kepler’s third law
Newton
• justified the Kepler-revised Copernican
model
• accurately predicted the motions of the
planets
• Impact of Newton’s Laws:
mathematical tool for:
– placing satellites in orbit around earth
– setting trajectories of spacecraft in solar system
– defining the escape speed on an object from a
planet (or the solar system itself)