Download A Short History of Space Science

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Module 4
Section 1
Lesson 1
A Short History of Space Science
Learning Outcomes
After completing this lesson, you will be able to

Name the philosopher/scientists and state their contribution to the study of
space science

Describe how a scientific model can change as more information becomes
available

Describe the terms geocentric, retrograde and epicycle.

Describe how the Greek philosophers overcame the problems that other
cultures experienced with mythology
Key Words
 Astronomy

Thales

Aristotle

Aristarchus

Ptolemy

Almagest

Geocentric

Retrograde

Epicycles

Astrolabe
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Resources
Books

The History of Science From the Ancient Greeks to the Scientific
Revolution Pages 3 – 29
National Geographic Picture Atlas of Our Universe

Birth of Astronomy Pages 9 - 13

Our Universe Pages 8 – 17
Internet
http://www.britannica.com/bcom/eb/article/5/0,5716,115385+3,00.html
The above resource is from Encyclopedia Britannica. It is an excellent
resource for short descriptions about space science. There is a free 14day subscription, which allows you to use the full encyclopedia.
http://www.lvaas.org/astronomy/main.html#5
This is a huge, general reference for space science. This resource comes
from the McGraw-Hill website.
http://www.school.mcgrawhill.ca/resources/sciencepower9/power_913.html
There are many good resource sites listed here.
http://www.astro.uni-bonn.de/~pbrosche/hist_astr/ha_pers.html
This extensive history of anyone involved in space science is remarkable.
http://csep10.phys.utk.edu/astr161/lect/index.html
http://csep10.phys.utk.edu/astr161/lect/index.html
Two excellent references for astronomy
Introduction
When you look at the sky after the sun has disappeared, it gradually becomes
filled with spots of light. Some spots are bright, some dimmer, but they fill the sky
with a beautiful array of light that number about 2000 at any given time.
The bright spots are planets, stars, galaxies and other celestial objects; some
give off a steady light and some blink.
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The last time you studied Space Science was grade six. At this time you learned
about the solar system and the Earth’s place in it. You also learned about space
research, Canada’s place in adding to knowledge about space, and the positive
and negative impacts of this research. Topics covering the cycles of day and
night, seasons and moon phases were studied.
This year you will measure some objects in space and learn how these
measurements were and are used on earth. You will study the motions of some
objects in space. You will attempt to answer questions such as, “How did the
universe begin?” and “What is a black hole?” Finally, you will take a look at
modern technology that is pushing back space frontiers and answering some
very interesting questions.
Your study in space science will begin with a history of how the ancient
philosopher/scientists began understanding and using the objects in the sky
above them.
The Beginning of Astronomy
About 4 000 years ago, Egyptians would look at the Sun as it moved across the
sky and understand that a sacred boat was taking the Sun god Ra from eastern
shore, travel across the heavenly ocean, set at its western shore and continue,
through the night, to travel through the underworld until it once again began its
journey from the East.
As time passed, hunters and farmers observed that the heavenly objects viewed
at night followed a pattern of movement. These hunters and farmers- we can call
them the first primitive astronomers- used the repetition of the patterns in the sky
to predict seasons. Accurate determination of seasons was important to their
survival. As a result, they began keeping accurate records, and developed charts
of sky patterns. The science of astronomy had begun.
Ancient civilizations, as demonstrated by Egyptian mythology, did not understand
the movements of stars and planets. The Egyptians, Babylonians, and others
had developed mathematical tools, made observations and kept records of their
observations, but they did not employ these tools to develop any models
concerning the cause of star and planet movement. Greek civilization was the
first to break away from mythology and superstition for several reasons:
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Greek civilization encouraged questioning minds. It was natural for a Greek to
ask “why”. You know from your perspective as a 21st century science student that
it is the nature of a scientist to ask the same question.
The city-state political structure in Greece had no strong central government to
dictate social structure or thought. As a result, the Greeks were conditioned to
question the mythology that surrounded their culture. The stage was set for an
advance from accepting gods that controlled their environment to one where
natural causes determined the motion of the heavens.
Thales
One of the earliest Greek astronomers was Thales. He was born around 624 BC.
The information we have about Thales is sketchy, but he is thought to have been
a merchant and businessman. Because of his occupation Thales probably
traveled widely and spent time in Egypt. Thales is considered to have been the
first of the Greek philosophers to move away from supernatural explanations of
the natural world. Thales said the earth floats on water and that all the different
parts of the earth, from mountains to trees were also made of different states or
forms of water. We know that his theory was not correct, but it does point out that
Thales had developed a theory that didn’t depend on mythology.
Aristotle
Aristotle was born on 384 BC, was a star pupil in Plato’s Academy in Athens, and
became the first person to develop a system to explain how the universe worked.
Aristotle affected science for centuries, and he showed that grand theories,
explaining the workings of the universe, were possible.
Aristotle’s stature as a philosopher was so great that his theories regarding all
aspects of science-not only astronomy- were generally regarded as being
absolutely correct for almost two millennia. Aristotle developed several concepts
with regard to the universe and the earth’s position in it.

Spheres that rotated around the Earth carried stars, planets and the sun.
The earth was a spherical ball in the center of the spheres and was
therefore the centre of the universe.

Stars were located on the inside of the largest sphere that rotated once a
day around the earth
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
planets were located on smaller, transparent spheres that rotated at
different speeds and on different axis. This could explain why planets
seem to move inside the stars. The transparent spheres explain why we
can see planets and stars.

The universe is perfect. The circle is a perfect geometric shape. The
planets and sun and all heavenly objects must move in circular paths
around the earth.
These first four concepts formed what Aristotle called the celestial sphere. You
can see from the diagram below that the stars were fixed on the inside of the
outer sphere. Earth is in the center of the sphere; the planets and Sun are
arranged around the Earth. The planets, sun and all objects in space revolved
around Earth in specific orbits at their own speeds.
We still use the celestial sphere today for navigation purposes. Any object in
space can be located as a point on a straight line drawn from Earth to a point on
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the outer sphere. If the outer sphere has coordinates placed on it, then we can
locate any object in space using these coordinates.

“Nature abhors a vacuum”, therefore, the universe must be filled with an
ether vapour.
Aristotle was a philosopher. A philosopher during this time of great intellectual
activity would try out ideas that seemed to explain the observed behaviour of
heavenly objects. If the ideas seemed to be in harmony with the observations
that were known at the time, or if they were “obviously correct”, they were
accepted as fact.
Aristarchus
Aristarchus was born on 310 BC, and became a brilliant mathematician who
spent a great deal of time studying the universe. Aristarchus is mentioned in this
brief history for two reasons. First, he was able, through painstaking observation,
to develop a remarkably accurate picture of some aspects of the universe 2 000
years ahead of his time. He was able to declare that the sun was a huge ball of
fire and that the sun, planets and stars did not revolve around the Earth, but that
the Earth and planets revolved around the Sun.
Secondly, Aristarchus is mentioned because he represents a common dilemma
at that time-whose theory do you believe? Aristarchus theory was not accepted
because it didn’t seem to fit observations. It seemed reasonable that if the Earth
were moving through space, they should feel the movement.
Hipparchus
Many consider Hipparchus the greatest of the Greek astronomers. He was able
to:

compile an extensive star chart using just his eyes. He included a
classification of stars according to their brightness. His star chart was
used for centuries.

He calculated the distance to the moon using parallax.

He discovered the existence of precession in which the axis of rotation of
the Earth changes over time.

Hipparchus developed a system of epicycles to help explain the
movement of planets in a geocentric system.
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Ptolemy
Ptolemy was born Claudius Ptolemaeus in 100 AD. His name was changed to
Ptolemy and it is by that name he is known today. Ptolemy is generally regarded
as the best astronomer in antiquity
Ptolemy presented his picture of the universe as we know it in a book called the
Almagest in which he summarized Greek knowledge up to that time. Ptolemy
spent many years studying Aristotle and Aristarchus. He chose to side with
Aristotle and describe a universe that was Earth centred. This is a good time to
stop and consider two developments:
The term Earth-centred is one that you learned in grade six science. We will use
a more scientific term and call it geocentric.
The men who had observed objects in the sky noticed there were some that
seemed to “wander”. These objects would travel in a east to west direction,
change direction to travel west to east for a period and then go back to the
original east to west direction. The apparent direction of motion for theses
objects was always measured against the background of the stars. The Greek
name for wander is “planet” and that is the name by which we know them to this
day. When a planet wanders backwards in terms of its initial motion, we call the
motion retrograde.
Ptolemy, with many philosophers of the time had difficulty with retrograde motion
because it didn’t tie in with Aristotle’s perfect universe. Ptolemy established a
complex theory of epicycles or little circles to explain the retrograde motion of
planets as seen from the earth. Ptolemy’s explanations for all the different
motions for all the different planets created a very complex theory that was
difficult to understand and use.
Early Greek measurements were carefully and accurately done. The
measurements were so good that discrepancies found many years later were
due to changes in the motion of objects in space and not to any errors in
measurement. One of the early Greek astronomers, Hipparchus, considered the
greatest of the ancient astronomers, was able to mathematically calculate the
size of the moon and its distance from the Earth. Hipparchus also created an
extensive star chart of 850 stars. Hipparchus’ observations led him to explain the
motion of planets as being outside of the center of Earth. Ptolomy would lean on
Hipparchus’ observations and mathematical models for his explanations for the
motion of planets.
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Ptolemy represented the decline of the great philosophers. Exploration of the
mysteries of the universe diminished for nearly 14 centuries as the culture that
spawned such great thinkers came to an end. The Roman era began with
Augustus Caesar in 27 BC. The Romans, however, were not scientists, but were
more concerned with finance, engineering and government. After the fall of
Rome in the 5th century, a long decline of western civilization began. During this
time the great library at Alexandria was destroyed and most of the works there
were burned.
All was not lost however, as the works of Aristotle and Ptolemy’s Almagest
reached Baghdad, one of the capitals of the Arab world. It was here, in fact that
Ptolemy’s work was so highly regarded that it was named Almagest or the “great
work”. Ptolemy’s Book 5 of the Almagest contains an account for constructing an
Astrolabe.
The Arabs were excellent observers. They soon refined an instrument that
allowed them to fix the position of stars with high accuracy. The instrument is
called an Astrolabe. Arab astronomers were able to gather extremely accurate
observations of star positions. In addition, Arab observations of planet motion
and eclipses were responsible for the beginning of a revolution in astronomy in
the Middle Ages. The Spanish king, Alphonso X was able to persuade Arab
astronomers to gather their observations and record them in what has come to
be known as the Alphonsine tables.
Summary
This brief history of astronomy demonstrates its roots in antiquity.
Questions
1. Read your notes and any reference material you have that describes the
meaning of geocentric, retrograde and epicycle. Once you have read your
reference material, write in your own words the meaning of the terms.
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2. a. How did Aristotle and Aristarchus differ in their theories about the structure
of the universe?
b. Why was it difficult for the philosophers to decide whether they should
believe Aristotle’s or Aristarchus’ theory about the structure of the universe?