2. Grade 6 Astronomy – Big Ideas
• Develop an understanding of the position of
Earth in Space with respect to its astronomical
“neighbours”
• Investigate space research programs involving
the human presence in space
• Investigate the astronomical causes (motions)
related to day/night, the seasons, moon phases,
and eclipse events
3. Grade 6 Astronomy – Big Ideas
• Investigate and describe points of reference
in the night sky (e.g., constellation patterns),
and account for the seasonal changes
observed
• Examine changing conceptions, historically,
about Sun, Earth, Moon and Stars (NoS)
• Provide descriptions of certain historical and
cultural views on the cosmos (e.g. cultural
astronomy, astrology) (NoS)
5. The Greek Mind….
• Much of the Greek method of thinking revolved
around philosophy instead of scientific
reasoning
• Greeks valued perfection and therefore any
models of the universe should involve the
perfect shape, the circle
• Greeks also had no reason to believe that the
Earth was not the center of the universe.
Completely reasonable at the time – and still
reasonable today!
• The only 'scientific' data they had available to
them was the motion of the Sun, Moon, and
planets, which were monitored heavily at the
time
Ptolemy ~140 AD
7. The Motion of the Planets
…A Problem Emerges
• A model of the universe
would be very simple except
for the fact that the planets
undergo a “looping” motion in
their movements as seen
from Earth
• Remember, in one night, all
planets still rise in the east
and set in the west
• However, if you keep track of
the planet's position versus
the background stars night to
night, you will see the planet
'move'
• The word 'planetos' means
wanderer in Greek
Retrograde Motion
Jupiter and Saturn (June 2000 – May 2001)
8. Ptolemaic Model
• In order to produce the
retrograde motion of the planets,
Ptolemy created a model with
little circles called epicycles
• All the planets orbited the Earth
in a perfect circle
• The planet itself made a smaller
orbit centered upon the larger
orbit around the Earth
• With the right timing, this model
can reproduce the retrograde
motion seen from Earth
11. Ptolemaic Model
• In Ptolemy's complete model,
each planet had its own orbit
around the Earth with its own
epicycle
– By changing the period of the
orbit and the epicycle, the model
could match observations
relatively well
• The Sun and the Moon
traveled around the Earth in
perfect circles
• The entire model was
composed of more than 80
circles and was very
complicated
‘Simplified’ Ptolemaic Model
12. Ptolemy’s Model Survives
• Since Ptolemy’s model matched
observations sufficiently and no contrary
evidence was produced, it was supported
for nearly 1,500 years!
• After all, if the Earth was moving, shouldn't
we feel it?
• On top of all this, the Dark Ages provided
relatively little advance in any natural
philosophies (sciences) for Europe
13. Astronomy in the ‘Dark Ages’
• While Europe was
enduring the “Dark Ages”,
Islamic nations were
experiencing a kind of
‘golden age’ of astronomy
• Much of the knowledge of
the Greeks was preserved
and expanded upon during
this time
• Many of the proper names
for stars are relics of this
era
– Rigel, Betelgeuse, Vega ...
and Zuben Al-genubi
14. “Flat Earth” Models ?
There was never a time in history when the concept
of a flat (disc-shaped) Earth was widely held, either
by priests, prophets, poets, philosophers, scientists,
or the common people…..it would be a myth to
assume this…..and we cannot perpetuate this myth
with our students. The idea has come almost
exclusively from literature.
15. So, what was known back then by the
Greek and Arab Cultures….and then
lost?
• The earth is round
• Circumference/diameter of the earth; distance to
the moon
• The solar system is heliocentric (“sun-centred”)
• An estimate of the distance to the sun (while
wrong, the Sun was much further away than
commonly thought)
• Length of the year to a high degree of accuracy
16. Nikolai Kopernik (1473-1543)
• “Who in this most
beautiful of temples
would put His lamp at
a better place than
from where it can
illuminate them all?.
Thus the Sun sitting
as on a Royal throne,
leads the surrounding
family of stars!”
17.
18.
19. The Copernican Revolution
• At the end of the Dark Ages, a
Polish Catholic priest named
Nikolai Kopernik (Copernicus)
came up with a new model of the
universe where the Earth was no
longer at the center
• The heliocentric (Sun centered)
model placed the Earth out of its
central position, yet still maintained
many of the observations we see
• The perceived elegance in his
model was that it was simpler than
Ptolemy’s model, and explained all
the stuff going on very well
Nikolai Kopernik (Copernicus) (1473-1543)
22. The Copernican Model – Retrograde Motion
In the Copernican model, retrograde motion is an
apparent effect caused by the Earth 'overtaking' an
outer planet in its orbit
23. The Copernican Revolution
• Even though the Copernican model was a ‘simpler’
representation of the solar system, it was not widely
accepted due to the incredible hold Ptolemy had on the
minds of 16th century astronomers
• While it did provide a much simpler description compared to
Ptolemy, it did not necessarily improve the predictive power
of the model
• The religious ideas of the time insisted upon Earth being the
center of the universe (why would God demote us away
from the centre of creation?)
• Copernicus’ works were published in Latin, which was
unreadable by the common public who had no theological
training
24. Galileo - The Observer
• A century after Copernicus’ work,
other “natural philosophers” began
to make strides toward making the
heliocentric model popular among
ordinary people
• Galileo was the first to use a
telescope to make detailed
observations of the sky – he was as
famous in Italy then as David Suzuki
is now in Canada
• Though he did not invent the
telescope, he made many working
prototypes and trained them on a
variety of celestial bodies Galileo Galilei (1564-1642)
25. Galileo's Observations - I
• Galileo used his telescopes to make
observations of many heavenly
objects
• The sketch to the right shows Galileo's
observations of the four largest moons
of Jupiter
• He noticed that the position of these
four moons changed night to night, as
if they were revolving around Jupiter
• These moons now bear his name
– The “Galilean” moons of Jupiter are:
• Io
• Europa
• Ganymede
• Callisto
26. Galileo's Observations - II
• Galileo also noticed that
Venus was not simply a
point of light, but actually a
disk – this was NEW!!
• He watched Venus go
through complete phases,
just like the Moon
• This cycle of phases can
only be satisfied by the
heliocentric model, not the
geocentric one – a critical
TEST!
The phases of Venus
27. Galileo's Observations - III
• Galileo also pointed his
telescope toward the Sun
– NEVER DO THIS – DUMB!!
• He discovered that the disk of
the Sun was not perfect and
was occasionally dotted with
small black spots
• By making daily sketches of
these spots, he was able to
determine that the Sun itself
was rotating – WOW!
28. Galileo's Influences….
• All of Galileo's observations were pointing towards a
HELIOCENTRIC view of the universe
• Galileo published his observations and conclusions in multiple
works, including some published in Italian to appeal to a wider
audience
• Galileo’s popularization of new ideas about the cosmos
threatened the status quo, and he was forced to stop publicly
teaching in favour of the heliocentric model, and sentenced to
house arrest for the rest of his life; he communicated with his
daughter regularly through letters (she had been given over to
cloistered monastic life at age 13)
• The seeds of the Copernican Revolution, however, had been
planted and by the mid-17th century, virtually all philosophers
and astronomers were committed to the Copernican model
