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CHANGING
IDEAS ABOUT THE SUN
Ancient Greek scholars from Thales to Aristotle developed
a complex and rich vision of the universe. Proof depended
upon philosophical and logical rigor in this culture.  The
Ancient Greeks did not use detailed observation and
experimentation, which is integral to modern science.
Photo to left: Plato and Aristotle from
a segment of Raphael's School of Athens
Aristotle's explanation of the physical
universe was well developed and well defended according
to the ancient Greeks. His views were consistent with
the ancient Greek culture. Aristotle described an Earth-centered
(geo-centered) universe with the Moon, Sun and all
heavenly bodies moving around the Earth. Aristotle
taught that the world below the moon was changing and
imperfect. It was composed of the elements; earth,
water, air and fire. These elements should not be confused
with the modern substances of the same names.
Aristotle taught that above the moon
the heavens were permanent and perfect. The heavenly
bodies must, therefore, be made of a perfect element
that Aristotle called aether (from which we get the
word ethereal). Later scholars, using Latin, called
this fifth element quinta essentia or 5th essential
(from which we get the word quintessential).  He
believed that aether or quinta essentia was the most
perfect element. The motion in the heavens was always
circular; a shape that Pythagoras had taught was perfect.
The Sun, therefore, was perfect and unchanging and
moved around the Earth in a perfect circle.
Photo: Christian Aristotelian Cosmos.
From Peter Apian, Cosmographia (1524)
 These
were the dominant ideas of educated persons in the
Western world until late in the seventeenth century.
In the thirteenth century, they became part of the
doctrine of the Holy Roman Catholic Church.
In the mid-1500's Copernicus ( ref
1, ref
2)offered an alternative to Aristotle's (and
the Church's) structure of the universe. He
proposed a Sun-centered (helio-centered) universe
rather than an Earth-centered universe.
In the 1600s Kepler (1, 2)
and Galileo challenged many of the teachings of Aristotle.
They used careful experimentation, rather than logic
alone, as proof. In 1609 Galileo built a telescope to
allow him to observe more detail in the heavens. The
methods and tools used by Kepler, Galileo and others
were revolutionary.
 
Photos above: Credit and Copyright IMSS-Firenze Seventeenth Century Telescope.
Wood, paper. (First photo length: 1360mm and second photo length: 920mm)
Galileo observed dark spots on the Sun
that moved. He concluded that the Sun was spinning.
With his simple telescope Galileo also observed moons
around Jupiter, rings around Saturn and mountains and
valleys on the Moon. With these observations and careful
experiments measuring motion of objects Galileo was
able to seriously challenge the Greek ideas that had
dominated Western culture for 2000 years. One of the
important changes in worldview was the nature of proof.
Logic alone would not be sufficient. Experimentation
and careful observation became essential to proof.
Galileo attacked two of Aristotle's primary teachings
about the heavens. Galileo showed that the heavens
were neither perfect nor unchanging. This is the beginning
of our understanding that the Sun changes. It is the
beginning of our careful observation of the Sun. The
image below shows a modern picture of the Sun in visible
light. The small dark dots are Sunspots.
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Website link to see an animation of the Sun over
a 10 day period.
 Many
individuals contributed to early research of these
strange spots on the Sun in the early 1600's. However,
sunspot activity decreased from 1645 until 1715. With
so few sunspots people lost interest. However, in 1843
Heinrich Schwabe discovered the number of sunspots
increased and decreased in a cycle.
The following graph shows the sunspot number from about
1610.
 The
vertical axis is the number of sunspots counted and
the horizontal axis shows the year in 10-year increments.
The pattern shows peaks of high sunspot number about
11 years apart. The long period with few sunspots occurred
during a period called the "Little Ice Age" in
which temperatures decreased globally. This coincidence
of the lack of sunspots with a decrease in global temperatures
is not sufficient proof of a cause-effect relationship.
It does raise interesting questions. More accurate
measurements have found the sunspot cycle to be, on
average, 11.1 years with ranges between 8 and 16 years.
Ground based telescopes and satellite-based
observatories are contributing much to our understanding
of the Universe. In particular, satellites launched
under the Sun-Earth
Connection (SEC) program have revealed much about
our local neighborhood. We now know that the Sun changes
on scales ranging from fractions of a second to billions
of years and from kilometers to tens of Earth radii.
What was the sunspot activity when you
were born or on any important date?
+
Website Link to find out
Or, become a Sunspotter and join the
Student Observation Network.
+
Website Link to Student Observation Network
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