Applied Science: Unit 14 A- astronomy and space science
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Astronomy and space science
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Astronomy And Space Science
Astronomy And Space Science: Stellar
Astronomy
Scientific Thought: In Context
COPYRIGHT 2009 Gale
Astronomy and Space Science: Stellar Astronomy
Introduction
Stellar astronomy is the study of the sun and the stars: what they
are, how they move, and how they are born, live, and die. The majo...
applied science unit 14 a astronomy and space science
astronomy and space science stellar astronomy scientific thought in context copyright 2009 gale astronomy and space science stellar astronomy
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ASTRONOMY AND SPACE SCIENCE
Astronomy And Space Science: Stellar
Astronomy
Scientific Thought: In Context
COPYRIGHT 2009 Gale
Astronomy and Space Science: Stellar Astronomy
Introduction
Stellar astronomy is the study of the sun and the stars: what they
are, how they move, and how they are born, live, and die. The major
challenge of this field is the staggering distance to even the closest
stars. Scientists had great difficulty understanding stars without
being able to touch them and experiment upon them. This difficulty
required radical, creative thinking and a constant willingness to
embrace new ideas and techniques.
Historical Background and Scientific Foundations
The motion of the sun, both on a daily and annual basis, is one of
the most basic human observations of the sky. Most ancient
civilizations developed techniques of varying sophistication for
tracking, recording, and predicting these motions for agricultural and
ritual purposes. Some devices have survived in the form of
structures, such as Stonehenge in England.
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Greek astronomers only investigated the stars as points against
which to measure the motion of the planets. Despite their limited
,tools, Greek astronomers were able to make impressive estimates
of the size and distance to the sun. Aristarchus of Samos (c.310–
c.230 BC) used the geometry of eclipses to calculate that the sun
was roughly 19 times as far away from Earth as the moon, and that
the sun was about 6fl the size of Earth. These numbers are far
smaller than modern values, but represent a significant
achievement of mathematics for their day.
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Physical understandings of the sun and stars were codified by the
Greek philosopher Aristotle (384–322 BC), whose cosmological
system remained intact and in use for nearly two thousand years.
Aristotle described the universe as a series of nested spheres, with
Earth at the center and the fixed stars at the outside. A critical
element of Aristotle's system was the lunar boundary: below the
boundary was the world of earth, air, fire, and water—a world that
was marked by constant change—and above it everything was
perfect and unchanging in every way. Thus both the sun and the
stars, being above the boundary, were thought to not change over
time (other than their circular motion). Any changes in the sky, such
as meteors, were assumed to be atmospheric phenomena.
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The Sun at the Center
Two factors, conceptual and observational, combined in the
sixteenth and seventeenth centuries to make the sun a focus of
interest. The first was the emergence of the idea that the sun was in
some way special. The stimulus for this elevation of the sun's
significance is usually attributed to the Polish astronomer Nicolas
,Copernicus (1473–1543), whose cosmological system placed the
sun at the center of the universe. Copernicus' motivations were
complex, but he argued that the sun was the most important
celestial body and that a central location was more fitting: “At rest, in
the middle of everything, is the Sun. For in this most beautiful
temple, who would place this lamp in another or better position than
that from which it can light up everything at the same time?”
One of Copernicus' most ardent followers, the German
astronomer Johannes Kepler (1571–1630), thought the central
location of the sun had important physical and theological
significance. He thought it might provide a physical force that moved
the planets. He made little progress with this idea, but it provided
the foundational concept that the sun had physical effects on the
planets. From his cultural background, Kepler also saw Christian
theological meaning in the structure of the Copernican cosmos.
The Parallax Problem
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Few of the early Copernicans gave serious thought to the nature of
the stars, but their cosmology did make an important prediction
about their appearance. If, as Copernicus claimed, the Earth
moved, then astronomers should be able to observe a phenomenon
known as stellar parallax. Parallax is the apparent motion of a
nearby object relative to a distant one as viewed by an observer
who is also in motion. An observer on a moving Earth should be
able to see nearby stars moving relative to distant stars on an
annual basis. This was not observed, however, and that meant
either that Copernicus was wrong, or the universe was vastly larger
than previously assumed, since parallax decreases with the
distance of the observed objects.
, In the years between Copernicus and Kepler, dramatic advances
were made in astronomical technology and technique that helped
overturn the Aristotelian understandings of stars and the sun. One
of the major figures was the Danish astronomer and
aristocrat Tycho Brahe (1546–1601). Tycho acquired an entire
island and used tremendous resources to build a sophisticated
observatory with massive versions of traditional instruments such as
the quadrant. His observations were vastly more accurate than any
made before, and two observations made a particular impact. The
first was in 1572 when he saw that a new star had appeared in the
sky (a nova); the second was a comet in 1577. Using his uniquely
precise tools and methods, Tycho was able to convincingly
demonstrate that both of these phenomena
Must have been above the moon. This indicated the celestial realm
was not unchanging as Aristotle had predicted.
It is interesting to note that the 1572 nova was the first recorded in
western astronomy, but several novae had been previously
observed and recorded by Chinese astronomers. This is a striking
example of how sometimes people, even trained astronomers, see
only what they expect to see: since Aristotle said changes among
the stars were impossible, observations of such changes were
simply rejected.
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A generation after Tycho, the Italian astronomer Galileo Galilei
(1564–1642) improved the design of the telescope, a new tool
invented in the Netherlands. He turned his telescope to the night
sky, observing a variety of phenomena not previously recorded. He
found that where the planets appeared as disks in the telescope,
the stars remained as tiny points. He interpreted this to mean that
they were much farther away than the planets, which he used to
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