Name
Date
Period
History of Astronomy Notes
Please be aware that these notes have been highly condensed from the original. To get a better and
deeper understanding read the full version at Nick Strobel's web site.
http://www.astronomynotes.com/history/s1.htm
Part I - Early History- The Early Greeks
A)
Believed logic and math could help uncover truths
B)
Ex. Socrates and Plato
The Greek paradigm (a general consensus of belief as to how the world works) at the
time was:
 The planets, sun and other celestial objects all move in perfectly circular orbits
 The speed of the orbits is perfectly uniform
 The Earth is at the exact center of the motion of all celestial bodies
Plato gave his students a problem to solve, find a geometric explanation for the motion of the
planets (means wanderer in Greek), including retrograde motion. (At times the planets appear to
reverse direction for a short time) Of course in thinking about this most students were stuck in the
Pythygorean paradigm. Aristarchus, however, came up with the idea that the sun was at the center
of the system. His idea was not accepted because it did not fit with the prevailing knowledge. It
was obvious to the Greeks that the Earth was not moving beause:
 Earth was not part of the heavens
 Celestial objects are bright points of light, whereas the Earth is a non-luminous rock
 The heavens did not change, whereas the Earth was always changing
 Our senses do not indicate any movement, if you jump up you land in the same spot.
We do not fly off the spinning Earth into the heavens
______________ took the view that scientific ideas are more than just tools and can be used to
explain the workings of the world (unlike Plato). Aristotle's idea was that the planets and stars were
on concentric crystalline spheres centered on the Earth. Each planet, the Sun, and the Moon were on
their own sphere. The stars were placed on the largest sphere surrounding all of the rest. Later
Greeks came up with the idea of epicycles to explain the backward motion of the planets. Ptolemy
perfected this idea. Draw the diagram of epicycles below.
The Earth centered view of the heavens remained pretty much unchanged for 1500 years. New
thinking finally began to emerge during the renaissance (French for re-birth). Prior to this time,
most notable undertakings in astronomy occurred in the Islamic world. Islamic astronomers were
careful observers of the sky and created accurate star catalogs and tables of planet motions. Many
of the names of the bright stars in our sky have Arabic names (e.g., Deneb, Alberio, Aldebaran,
Rigel to name a few).
In the 16th century the paradigm of man's place in the universe was as follows:
 Man is God's special creation in the universe


Earth is at the center of a mathematically perfect universe
Using logic and reason man is given the gift of being able to read this harmony
It is important to understand this background as we move forward in time because it will help you
to perceive the motivations of individuals and why certain ideas clashed so violently with others.
In you own words, write down an explanation of Occam's razor-
Nicolaus ____________ - Felt that the geocentric view with all its epicycles was too messy to be
a creation of God. He also came to believe that the sun (source of life-giving energy) was a good
material copy of God and therefore should be at the center of the universe. He therefore resurrected
Aristarchus' idea of a heliocentric or sun-centered system. However, he was still enveloped in the
prevailing paradigm that the movements of all heavenly bodies must be circles because circles are
the perfect shape and God would only create a perfect universe. Thus, his heliocentric model still
had small epicycles in it so that it would match with actual observations of the planets.
What is retrograde motion?
Many astronmers of the period did not agree with Copernicus. If the Earth were moving, why then
don't we see a parallactic shift? A parallactic shift is the idea that the apparent position of a star
should shift relative to the other stars when seen from Earth's position in space 6 months apart.
(remember the thumb over the object eye shift example here) [they did not see the shift because
their instruments were not accurate enough to measure it, also they could not conceive of God
wasting so much space and leaving such huge gaps between stars]
Tycho Brahe - A man with most excellent observations!! Tycho did not go for Copernicus's
heliocentric model. He stuck with the Geocentric model and made the math work. He made
thousands of extremely accurate observations (all without a telescope!) of the planets and the stars
and recorded all his observations in notebooks. It is ironic that his own meticulous notes would
later prove essential in showing that the heliocentric model was a better representation of our solar
system.
During this time the idea of the perfect heavens (circles, etc.) and the imperfect Earth was held and
taught by the Catholic church. Any ideas to the contrary were met with severe consequences.
Remember, this is roughly the same time as the Inquisition.
Giordano Bruno (lived 1548--1600 C.E.) revived Democritus' (a contemporary of
Socrates) view that the Sun was one of an infinite number of stars. This infinite
sphere was consistent with the greatness of God. Bruno believed in a heliocentric
universe. He believed that God gave each of us an inner source of power equal to all
others, so there was no justification for domination and servitude. His model had
definite political ramifications that threatened the Church's political authority.
After eight years in a prison in Rome, and after failing to get him to recant, the church took him to
the town square and burned him at the stake.
Galileo ____________ (1564--1642 C.E.) was the first person we know of that used the telescope
for astronomical observations (starting in 1609). The telescope was originally used as a naval tool
to assess the strength of the opponent's fleet from a great distance. He found many new things when
he looked through his telescope:
 He saw many new fainter stars that no one had seen before
 He saw pits and craters on the moon and spots on the sun, this meant that the Earth was
not the only place change and decay
 He discovered 4 moons going around Jupiter! This completely flew in the face of the
idea that everything had to go around the Earth
 He discovered that Venus goes through phases like our moon. This could only happen
in a heliocentric model where Venus changes positions relative to the Earth while it goes
around the sun.
Galileo's ideas got him in trouble with the church. He spent his last years under house arrest.
Johaness Kepler (lived 1571--1630 C.E.) was hired by Tycho Brahe to work out the mathematical
details of Tycho's version of the geocentric universe. However, Kepler preferred the heliocentric
model. He was having a very difficult time getting Brahe's data to fit the Copernicun model until
he was able to shake the Pythagorean paradigm of the circle as the perfect shape. For the first time
in history a shape for the orbits was considered other than the circle. This shape is an
____________.
What is Kepler's 1st law?
Draw and label the diagram of the elliptical orbit:
The eccentricity of an ellipse is a measure of how "out of round" it is. A circle has an eccentricity
of ___ and a straight line has an eccentricity of ___. The eccentricities of the planets are very close
to 0 and so Brahe's very careful observations were very important in helping Kepler to discover this
fact. Kepler went on to name two other very important laws of planetary movement that are still
used today in astronomy.
With Kepler's 3 laws astronomers were able to explain many of the movements of objects in space.
Finally an explanation was in place that fit with all the data. The heliocentric model of the solar
system was here to stay. Further refinements and improvements in instruments have only further
validated the ideas of Kepler. Remember, however, as with all ideas in science, we always leave
open the possibility
for change. Scientific ideas can never be proven correct, they can only be proven incorrect.
See the "problem of induction" web page for a great explanation and example.
http://www.astronomynotes.com/scimethd/s4.htm