Download Geocentric Model of the Solar System

Chapter 26.2: Observing the
Solar System
Early views of the organization of
Space were much different than ours.
Early astronomers believed that the Earth was the
center of our Universe, and that the Earth was
surrounded by a ball, called a Celestial Sphere, on
which were fixed most of the objects of the heavens.
This interpretation of our solar system is called a
Geocentric Model, meaning Earth-centered.
Early astronomers noticed groups of stars that were visible
at the same time every year. These were named
constellations, and were used as a basis for calendars.
The Orion
Constellation
Astronomers noticed that some celestial bodies
did change position relative to the constellations.
They called these “wandering stars” planets.
Notice the planet Mars moving across the constellations Gemini and
Leo over the course of 11 months.
Astronomers also noted that,
periodically, these planets which
normally moved eastward,
moved backward for a few
weeks, then resumed their path
eastward. This is referred to as
retrograde motion.
In 200 A.D., the Greek astronomer Ptolemy explained
this “retrograde’ motion by stating that the planets
orbited the Earth in a circle, but also orbited another
point in a circle, what he called an epicycle.
In the late 1400’s, the astronomer Copernicus
proposed what was to become known as the
Heliocentric Model.
Copernicus stated that the Sun was the center of
the Solar System, the Earth was a planet, and
that it orbited the Sun.
And, here is how he explained retrograde
motion.
Mars retrograde motion
Venus retrograde motion
In the 16th –century, the astronomer Johannes
Kepler developed three laws to describe the way in
which planets move through Space.
Kepler’s 1st Law: Planets move through Space in an
elliptical orbit, not a circular one. This causes the
distance from a planet to the Sun to vary.
Kepler’s 2nd Law: When a planet is closer
to the Sun, it moves faster. (centrifugal
force and gravity at work!)
Kepler’s 3rd Law states that the further a
planet is from the Sun the longer its period
of revolution (its year) will be.
In the 1600’s, Isaac Newton stated that a force
called gravity was causing the planets to behave
as Kepler had observed.
He stated that all objects with mass exerted a force of
attraction on other objects with mass, and that the
strength of that force is proportional to the mass of the
objects and their distances from one another.
Early Astronomers
Astronomers
Ptolemy
•devised the geocentric
model for our solar system
believed until 1500's
•said planets are on small
circular orbits, called
epicycles
•developed 1st model to
predict the positions of
planets
AD 90-168
•had support of Catholic
church, despite inaccuracy
•challenged Ptolemy's
geocentric model and
proposed the heliocentric
model for our solar system
Copernicus
•suggested the Earth was a
planet, it rotated, and that
Earth & other planets
revolved around the sun
•tried to explain retrograde
motion (i.e. when 2 bodies
move the same direction &
one moves faster than the
other
1473-1543
Johannes
Kepler
1571-1630
•discovered that planets orbit in
ellipses, not circles
•developed 3 laws of planetary
motion
1."planets travel in elliptical
orbits with the sun at one focus
& the planet's distance from the
sun varying"
2.equal area law= "the speed
at which the planet travels
around the sun is not constant;
planets closer to the sun orbit
faster than those further away"
3.harmonic law= "the period of
a planet squared is equal to the
mean distance cubed“
P squared= D cubed
•explained why we don't
feel the Earth moving
Galileo Galilei
1564-1642
•first to use a telescope;
invented refracting
telescope
•discovered Jupiter's 4
largest moons and proved
that they revolved around
Jupiter disproving
geocentric model
Isaac Newton
•incorporated a mirror into Galileo's
telescope(refracating telescope),
doubling its power (reflecting
telescope)
•said that gravity keeps the planets
in orbit- supported by his 3 laws of
motion
1642-1727
•Newton's 3 laws of motion:
1.an object at rest stays at rest
until another force acts on it
2.the greater the mass of an
object being accelerated, the
more force needed to accelerate
the object
3.for every action, there is an
equal but opposite reaction
Joseph Von Fraunhofen
•invented the spectroscope
•invented many telescopes
and optical instruments to
describe stellar parallax
1787-1826
•Analyzed light
(spectroscopy) to
determine chemical
composition of stars
Albert Einstein
1879-1955
•Theory of Relativity:
adds the effect of gravity of
large masses to light and
time
(predicts black holes)
•corrected Newton's theory
of gravity by saying that
not all objects attract all
other objects
•E= mc2
Hubble Telescope
In orbit since April 24,
1990
•Hubble's Law: all objects in
deep space possess Dopplar
shift and this shift is proportional
to their distance from Earth.
•demonstrated the existence of
other galaxies than our own
•with Dopplar shift, he proved
that our universe is expanding
and continuously moving away
from us
Edwin Hubble
1889-1953
•disccovered and analyzed
"cosmic background radiation"
which supports Big Bang Theory