Transcript Volcanoes and Igneous Activity Earth

Chapter 22
“The Origin of
Modern
Astronomy”
Chapter 22.1 “Early Astronomy”
 Astronomy
• Astronomy is the
science that
studies the
universe.
• It includes the
observation and
interpretation of
celestial bodies and
related phenomena.
Ancient Greeks
 Golden Age of Astronomy
• The “Golden Age” of
early astronomy
centered in Greece from
600 – 150 B.C.
• The Greeks used
philosophical arguments
to explain natural
phenomena, however
they also relied on
observations of the
night sky.
Ancient Greeks
 Golden Age of Astronomy
• The Greeks used
instruments to make
these observations
such as the astrolabe.
• They also developed
the basics of
geometry and
trigonometry and
applied them to
An astrolabe was made of brass
astronomical
and used for determining the time
measurements.
and position of the Sun and stars.
Ancient Greeks
 Aristotle 384 – 322 B.C.
• Aristotle was a famous
Greek philosopher that
concluded that the Earth
was round because it
always casts a curved
shadow when it passes
between the sun and the
moon.
• This idea was popular until
the Middle Ages.
Ancient Greeks
 Aristotle 384 – 322 B.C.
• Aristotle also
believed the Earth
was at the center
of the universe and
surrounded by
spheres.
• He thought that
the closest spheres
contained the four
elements: earth,
air, fire, and water.
Ancient Greeks
 Eratosthenes 276 – 194 B.C.
• Eratosthenes made the
first successful attempt
to establish the size of
the Earth.
• He observed the angles of
the noonday sun in two
Egyptian cities that were
roughly north and south
of each other – Syene and
Alexandria.
Calculating Earth’s Circumference
Eratosthenes figured
the circumference of
Earth must be 50
times the distance
between these two
cities by finding that
the angles of the
noonday sun between
the two cities differed
by 7 degrees or 1/50th
of a circle.
•
Eratosthenes calculation of the Earth’s circumference was
39,400 km., which is very close to the actual circumference
of 40,075 km.
Ancient Greeks
 Hipparchus 190 – 120 B.C.
• Hipparchus was best
known for his star
catalogue in which he
carefully located and
plotted the positions
and brightness of
almost 850 stars.
• He divided the stars
into 6 groups based on
brightness.
Ancient Greeks
 Hipparchus 190 – 120 B.C.
• Hipparchus also
measured the length
of the year to within
minutes of the
modern year and
developed a method
for predicting the
times of lunar
eclipses to within a
few hours.
Ancient Greeks
 Geocentric Model (Earth-Centered)
• In the ancient Greeks’ geocentric model of the
universe, the moon, sun, and the known planets:
Mercury, Venus, Mars, and Jupiter orbit the
Earth.
Ancient Greeks
 Geocentric Model
•
The Greeks believed the Earth was a sphere that
remained motionless at the center of the universe.
• Beyond the planets, they believed there was a
transparent, hollow sphere of fixed stars which
traveled daily around the Earth called the celestial
sphere.
• The Greeks also believed that all heavenly bodies
remained in the same relative position to one
another, except the seven “wanderers” which were:
the sun, the moon, Mercury, Venus, Mars, Jupiter,
and Saturn.
Ancient Greeks
 Aristarchus 312 – 230 B.C.
•
•
•
Aristarchus was the first Greek
to believe in a sun-centered
universe.
He used geometry to calculate
the relative distances between
the Earth, sun, and moon.
He later used these distances to
calculate the size of the sun and
the moon, but his measurements
were much too small.
Ancient Greeks
 Heliocentric Model (Sun-Centered)
•
In the heliocentric model, Earth and the other 5 planets orbit
the sun.
Celestial Sphere of fixed stars.
Geocentric and Heliocentric Models
Picture A
Picture B
• Despite the fact that there was enough evidence to
support the heliocentric model, the geocentric model
dominated Western thought for nearly 2000 years.
Ancient Greeks
 Claudius Ptolemy 85 – 165 A.D.
• Much of our knowledge of
Greek astronomy comes
from Claudius Ptolemy.
• Ptolemy created a model of
the universe that accounted
for the movement of the
planets, which he published
in a 13-volume work in 141
A.D.
Ancient Greeks
 Ptolemaic System
• Ptolemy noticed that the
planets moved slightly
eastward among the stars
each night and even
appeared to stop and
reverse direction for a
time before resuming
eastward.
• He created a model of the universe that accounted for this
movement of the planets called the Ptolemaic System.
Retrograde Motion
 Ptolemaic System
•
This movement, called retrograde motion, is the apparent
westward motion of the planets with respect to the stars.
• This apparent motion occurs because the Earth has a faster
orbital speed than the other inner planets as they all revolve
around the sun.
• Ptolemy used small
circles called epicycles,
on which the planets
traveled as they
revolved around the
Earth, in order to
explain the retrograde
motion of the planets.