|
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.
+ 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
+ Back to Sun &
Earth Background | +
Top | + Next A
Star is Born
|
