Transcript Chapter 3.1 – Observing the Solar System I. Earth at the Center A

Chapter 3.1 –
Observing the Solar System
I. Earth at the Center
•
A. Greek Observations
•
1. Stars
–
When the Greeks observed the sky at night they
saw that the stars moved across the night sky but
the patterns of the stars were the same.
–
In other words, the stars stayed in a fixed position to
one another. The patterns or fixed positions of the
stars are called constellations.
Picture of Orion the Hunter
– There are certain constellations that are
present during certain seasons of the year
(such as the constellation Leo during the
summer).
– There are some constellations present all year
(such as Ursa Major).
– Constellations present all year round are
called circumpolar constellations.
2. Planets
– Besides seeing constellations of stars, the Greeks
also saw points of light moving in and around the
constellations.
– These moving points of light were called planets,
which means 'wanderers" in English.
– The Greeks made very accurate drawings of the
movements of these planets around teh sun. They
were only able to see six (6) of the eight (8) planets
we know today.
– The Romans named the six visible planets
based upon their size and color:
•
•
•
•
•
Mercury (The Messenger of the Gods)
Venus (Goddess of Love and Beauty)
Mars (God of War)
Jupiter (King of all the Gods)
Saturn (God of Agriculture)
• Based upon the Greek drawings, they
incorrectly assumed that the Earth was the
center of the universe and stationary.
• They assumed that everything else in the
universe (planets, Sun, and stars)
revolved around the Earth.
• It was known as the Geocentric System
(Geo means Earth in Greek).
Geocentric System
B. Ptolemy's Model
– In 140 AD, the Greek astronomer Ptolemy
developed a new model of the universe.
– He found that the planets moved in small
orbiting circles around themselves.
– However, he believed that the planets and
their small orbits are part of one large orbit
that had the earth as the center.
Ptolemy’s Model
II. Sun At the Center
– Not all Greek astronomers believed that the
Earth was the center of the universe.
– From their own drawing of the movement of
the planets, stars and Sun, the group of
astronomers believed that the Sun was the
center of the universe and everything in the
universe revolved around it.
– This view of the universe is called the
Heliocentric System (Helios is Greek for Sun).
A. The Copernican Revolution
– In 1542, a Polish astronomer named Nicolaus
Copernicus further refined the Heliocentric System.
– He added the Heliocentric System the arrangement of
the known planets in space and how such planets
moved around the sun in perfect circles.
– Since most powerful institutions such as the Roman
Catholic Church at that time believed that the
universe was geocentric, Copernicus waited until his
death to publish his findings about the universe being
heliocentric.
Heliocentric System
B. Galileo's Evidence.
• Using the compound telescope, Galileo
was able to track the exact orbits of the
moon, planets and the Sun.
• His scientific data gathered from his
observations of Jupiter and Venus proved
that the universe is heliocentric.
1. Jupiter
– Through the compound
telescope, Galileo saw that
Jupiter had at least 4
moons. Today we call
these 4 observable moons
the Galilean Moons.
– He noticed that the four
moons did not orbit the
Earth. Instead, the four
moons only orbited Jupiter.
2. Venus
• Galileo also tracked the
orbital pattern of Venus.
• He found that Venus did
not orbit the Earth but it
did orbit the Sun.
• Venus's orbital path
around the Sun was the
same as the Earth's orbit
around the Sun.
C. Tycho Brahe's Observations
• Tycho Brahe was an
astronomer who observed the
solar system patterns and
paths for over 20 years.
• Brahe confirmed the findings
that the universe was
heliocentric but he did not see
the planets in perfectly circular
orbits around the sun.
• Instead, he suspected that the
planets orbit the sun in an
elliptical or oval shape, but
died before he could test out
his theory.
D. Kepler's Calculations
• Brahe's assistant was
Johannes Kepler. Kepler
carried on Brahe's work and
tested his theory about the
orbits of the planets around the
sun being elliptical in nature.
• Kepler took careful
mathematical measurements
of Mars orbiting the Sun.
• Looking at the data Kepler
realized that the shape of the
orbit was an ellipse and not a
perfect circle.
III. Modern Discoveries.
• Today we refer to the universe as the "solar
system" - a Sun-centered system.
• We have also discovered three more planets
after Saturn: Uranus, Neptune, and Pluto.
• Scientists have also discovered other objects in
space such as comets, stars and asteroids.
Some of these are also in the orbits revolving
the sun.
–Since 2006, Pluto is no longer considered a
planet.
–It is a planetoid or dwarf planet because of
its small size and mass.