Download Astronomy: The Original Science

Astronomy: The Original
Science .
I
•
Objectives
Identify the units of a calendar.
Describe two early ideas about the
structure of the universe.
Describe the contributions of Brahe,
Kepler, Galilee, Newton, and Hubble
to modern astronomy .•
Terms to Learn
astronomy
year
month
day
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Reading Organizer As you read this
section, make a flowchart of the
development of astronomy.
astronomy
universe
the study of the
year the time required for the Earth
to orbit once around the sun
Figure 1 This building is
located at Chich en ttza in the
Yucatan, Mexico. It is thought
to be an ancient Mayan·
observatory.
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Chapter 1
Imagine that it is 5,000 years ago. Clocks and modem
calendars have not been invented. How would you tell the
time or know what day it is? One way to tell the time is to
study the movement of stars, planets, and the moon.
People in ancient cultures used the seasonal cycles of the stars,
planets, and the moon to mark the passage of time. For example, by observing these yearly-cycles, early farmers learned the
best times of year to plant and harvest various crops. Studying
the movement of objects in the sky was so important to ancient
people that they built observatories, such as the one shown
in Figure 1. Over time, the study of the night sky became the
science of astronomy. Astronomy is the study of the universe.
Although ancient cultures did not fully understand how the
planets, moons, and stars move in relation to each other, their
observations led to the first calendars.
Our Modern Calendar
The years, months, and days of our modern calendar are based
on the observation of bodies in our solar system. A year is the
time required for the Earth to orbit once around the sun. A
month is roughly the amount of time required for the moon
to orbit once around the Earth. (The word month comes from
the word moon.) A day is the time required for the Earth to
rotate once on its axis.
Who's Who of Early Astronomy
Astronomical observations have given us much more than
the modern calendar that ,:,e use. The careful work of early
astronomers helped people understand their place in the universe. The earliest astronomers had only oral histories to learn
from. Almost everything they knew about the universe came
from what they could discover with their eyes and minds.
Not surprisingly, most-early astronomers thought that the universe consisted of the sun, the moon, and the. planets. They
thought that the stars were at the edge of the universe. Claudius
Ptolemy (KLAWdee uhs TAHLuh me e) and Nicolaus Copernicus
(NIK uh LAYuhs koh PUHR ni kuhs) were two early scientists
who influenced the way that people thought about the structure of the universe.
a division of the year that
is based on the orbit of the moon
around the Earth
month
day the time required for Earth to
rotate once on its axis '
Ptolemy: An Earth-Centered Universe
In 140 ct, Ptolemy, a Greek astronomer, wrote a
book that combined all of the ancient knowledge
of astronomy that he could find. He expanded
ancient theories with careful mathematical calculations in what was called the 'Ptolemaic theory.
Ptolemy thought that the Earth was at the center
of the universe and that the other planets and
the sun revolved around the Earth. Although the
Ptolemaic theory, shown in Figure 2; was incor. rect, it predicted the motions of the planets better
than any other theory at the time did. For over
1,500 years in Europe, the Ptolemaic theory was
the.most popular theory for the structure of the
universe.
Figure 2 According to the
Ptolemaic theory, the Earth is
at the center of the universe.
Copernicus: A Sun-Centered Universe
In 1543, a Polish astronomer named Copernicus
published a new theory that would eventually
revolutionize astronomy. According to his theory,
which is shown in Figure 3, the sun is at the center
of the universe, and all of the planets-including.
the Earth-orbit
the sun. Although Copernicus
correctly thought that the planets orbit the sun,
his theory did not replace the Ptolemaic theory
immediately. When Copernicus's theor
was
accepted, major changes in science and society
called the Copernican revolution took place.
~
What was Copernicus's theory?
(See the Appendix for answers to Reading Checks.)
Figure 3 According to
Copernicus's theory, the sun is
at the center of the universe.
Section 1 Astronomy: The Original Science
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Tycho Brahe: A Wealth of Data
In the late-1S00s, Danish astronomer Tycho
Brahe (TIE koh BRAW uh) used several large
tools, including the one shown in Figure 4, to
make the most detailed astronomical observations that had been recorded so far. Brahe
favored a theory of an Earth-centered universe
that was different from the Ptolemaic theory.
Brahe thought that the Sun ,~nd the moon
revolved around the Earth and 'that the other
planets revolved around the sun. While his
theory was not correct, Brahe recorded very
precise observations of the planets .and stars
that helped future astronomers .
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Johannes Kepler: Laws of Planetary
Motion
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After Brahe died, his assistant,· Johannes
Kepler, continued Brahe's work. Kepler did not
agree with Brahe's theory, but he recognized
how valuable Brahe's data were. In 1609, after
analyzing the data, Kepler announced that
all of the planets revolve around the sun in
elliptical orbits and that the sun is not in the
exact center of the orbits. Kepler also stated
three laws of planetary motion. These laws
are still used today.
Figure 4 Brahe (upper right) used a mural
quadrant, which is a large quarter-circle on a wall,
to measure the positions of stars and planets.
Galileo: Turning a Telescope to the Sky
In 1609, Galileo Galilei became one of the first people to use
a telescope to observe, objects in space. Galileo discovered
craters and mountains on the Earth's moon, four of Jupiter's
moons, sunspots on the sun, and the phases of Venus. These
discoveries showed that the planets arenot "wandering stars"
but are physical bodies like the Earth.
'
Isaac Newton: The Laws of Gravity
In 1687, a scientist named Sir Isaac Newton showed that
all objects in the universe attract each other through gravitational force. The force of gravity depends on the mass of the
objects and the distance between them. Newton's law of gravity
explained why all of the planets orbit the most massive object
in the solar system-the sun. Thus, Newton helped explain the
observations of the scientists who came before him.
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How did the work of Isaac Newton help
explain the observations of earlier scientists? ';
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Chapter 1
StudyingSpace
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Modern Astronomy
The invention of the telescope and the description of gravity
were two milestones in the development of modern astronomy.
In the 200 years following Newton's discoveries, scientists made
many discoveries about our solar system. But they did not learn
that our galaxy has cosmic neighbors until the 1920s.
Edwin Hubble: Bey~nd the Edge of 'the Milky Way,
Before the 1920s,' many astronomers thought that our galaxy,
the Milky Way, included every-object in space. In 1924, Edwin
Hubble proved that other galaxies existed beyond the edge
of the Milky Way. His data confirmed the beliefs of SOme
astronomers that' the universe is much larger than out galaxy.
Today, larger and better telescopes on the Earth and in spate,
new models of the universe, and spacecraft help astronomers
study space. Computers, shown in Figure 5, help process data
and control .the movement of telescopes. These tools have
~ helped answer many questions about the universe. Yet new
'technology has presented questions that were unthinkable
even 10 years ago.
,.~
,
Using J(ey
erms
1. Use each of the following terms
in a separate sentence: year, day,
month, and astronomy.
Understanding
Key Ideas
2. What happens in 1 year?
Astronomy, the study of
the universe, is one of /,
the oldest sciences.
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The units of the modern
calendar-days, months,
and years-are based
on observations of
objects in space.
Ptolemaic theory states
that the Earth is al.·the
center of the universe.
Copernican theory states
that the sun is at the
center of the universe.
'Modern astronomy has
shown that there are billions of galaxies. ' ,
a. The moon completes one
orbit around the Earth.
b. The sun travels once around
the Earth.
c. The'Earth revolves once on its
axis.
d. The Earth completes one orbit
around the sun.
3. What is the difference between
the Ptolemaic and Copernican
theories? Who was more accurate: Ptolemy or Copernicus?
4. What contributions did Brahe
and Kepler make to astronomy?
5. What contributions did Galileo,
Newton, and Hubble make to
astronomy?
Figure 5 Computers are,
used to control telescopes and
process large amounts of data.
Math Skills
6. How many times did Earth orbit
the sun between 140 cs, when
Ptolemy introduced his theories,
and 1543, when Copernicus
introduced his theories?
Critical Thinking
7. Analyzing
Relationships
What
advantage did Galileo have over
earlier astronomers?
8. Making
Inferences Why is
astronomy such an old science?
For a variety of links related to this
chapter, go to www.scilinks.org
Topic: The Stars and Keeping Time;
Early Theories in Astronomy
SciLinks code: HSM1449; HSM0444
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