Download The History of Astronomy

The History of Astronomy
brought to you by:
Mr. Youngberg
The Geocentric View
• All motion in the heavens is uniform circular motion.
• The objects in the heavens are made from perfect
material, and cannot change their intrinsic properties
(e.g., their brightness).
• The Earth is at the center of the Universe.
• Prograde motion: forward motion
• Retrograde motion: backward motion
Aristotle’s Theory
384-322 BC
• Geocentric view
dominated thinking for
1800 years.
• Earth is made up of only
four elements: earth,
water, air, and fire.
• The celestial bodies were
perfect and divine, and
made of a fifth element
called Aether.
Aristotle’s Cosmological System
• Universe is made up
of 55 celestial
spheres.
• Each sphere rotates
• Outside the spheres
is the prime mover
that caused the
rotation.
Claudius Ptolemy
87 – 150 A.D.
• Geocentric view of the
Universe
• Explained retrograde
motion of the celestial
bodies.
• Used over 80 epicycles
to explain the motions of
the Sun, the Moon, and
the five planets known in
his time
Ptolemaic System
• The planets’ move on
large circles around
the Earth- the deferent
• The planets travel on
small circles called
epicycles that move on
the larger circles.
• Explained retrograde
motion and brightness
variation.
Nicolaus Copernicus
1473-1543
• Heliocentric theory of
Universe: Sun Centered
• Earth is not stationary
• Earth turns on its axis
once a day!
• Still used a few epicycles
to explain backward
motion
The Copernican Universe
Retrograde Motion in the Copernican System
Tycho Brahe
1546-1601
•
•
•
•
Most precise observations
with the best instruments
available, prior to telescope
Observations of planetary
motion, lead to our current
model of the solar system.
Observations of a Supernova in 1572. No parallax so
therefore a star, and a
change in the heavens!
Observed a comet in 1577.
Used parallax to prove
distance. Conflict!
Johannes Kepler
1571-1630
• Heliocentric View
• Worked under Brahe and
used his observations to
devise his three laws of
planetary motion
• Planets orbit the Sun in
ellipses with the Sun as
one focus.
• The closer a planet is to
the sun, the faster its
speed.
Kepler’s
st
1
Law
I. The orbits of the planets are ellipses, with
the Sun at one focus of the ellipse.
Kepler’s
nd
2
law
The line joining the planet to the Sun sweeps out
equal areas in equal times as the planet travels
around the ellipse.
Kepler’s
rd
3
Law
The ratio of the square of the period of revolution is
proportional to the cube of the semimajor axis of
the ellipse.
Galileo Galilei
1564-1642
• First person to
successfully use a
telescope
• The sun had dark patches,
now called sunspots
• Four points of light
(moons) orbit Jupiter
• Venus has phases
• Observations paved the
way for Heliocentric
Phases of Venus
Isaac Newton
1642-1727
• Three laws of motion
described all motion
whether on Earth or in the
Heavens.
• Proved that Kepler’s three
laws were special cases of
Newton’s Laws
• Invented Calculus and the
Newtonian telescope.
Gravity!
• Observed an apple
accelerating toward the
ground.
• Called this force gravity!
• Extended this force from a
tree to the Moon.
• Every object in the
Universe attracts every
other objects (G)
• On Earth g = 9.8 m/s/s
Albert Einstein
1879-1955
-Special Theory of
Relativity: the speed of
light- 300,000 km/s- is an
important constant that
cannot be exceeded.
-General Theory of
Relativity: The presence
of mass curves space.
Special Theory General Theory
Matter and Energy
and Equivalent
m=mass
c=speed of light
History Quiz
1. Which astronomers believed the
Heliocentric view of the universe?
• Copernicus, Kepler, Galileo, Newton,
Einstein
2. Which astronomers believed the
Geocentric view of the universe?
• Aristotle, Ptolemy, Brahe
History Quiz
3. Which model believed that all heavenly bodies
were perfect and had perfect motion?
Geocentric
4. Who introduced the elliptical orbit?
Kepler
5. Whose theories break down near the speed of
light or near very massive bodies?
Newton
The End
References:
• Astronomy 161 The Solar
System
• Journey Through the Universe
• And more…