The rings of Saturn as observed by the robotic Cassini spacecraft looking back
toward the eclipsed Sun. Saturn's E ring is created by the newly discovered
ice-fountains of the moon Enceladus.
Homework #1 will be posted soon. An
announcement and instructions will be sent to
the class once it is posted.
“home”
We will be conducting a scientific
inquiry, so…
What is science?
Why does the University consider it
important for non-science majors to
take a course in the physical sciences?
There are many definitions of science. They all
have in common the view that
science encompasses those human
endeavors that seek to understand how
nature works.
“Scientific Thinking”
●
●
●
a natural part of human behavior.
We draw conclusions based on our
experiences & knowledge.
Progress is made through “trial and error.”
The Nature of Science
● Science
seeks explanations for observed phenomena
that rely solely on natural
causes.
● Science progresses through the creation and testing
of models of nature that explain the observations as
simply as
possible.
●A
scientific model must make testable predictions that
could force us to revise or abandon the model.
Theory -- a model which survives repeated testing
“Testable”
science, nonscience & pseudoscience
Testing separates science from nonscience: e.g., religion
is not accessible to experimental verification
Testing invalidates pseudosciences: e.g., astrology fails
testing.
Science attempts to systemized knowledge through:
 observing (what are the “observed facts”)
 questioning (framing the question)
 hypothesizing (knowledge of how nature works)
 testing (hypothesis makes predictions)
Thus, scientific thinking has applications to all fields of
human endeavors, not just science.
You will be shown a time sequence of
images showing the phases of the Moon.
Working with people near you to …
1. describe how the Moon’s appearance
changes from one full moon to the next.
2. come up with a physical explanation to
explain what you see.
Science begins with
observation:
 observing (what are the “observed facts”)
 questioning (framing the question)
 hypothesizing (knowledge of how nature works)
 testing (hypothesis makes predictions)
The origins of astronomy and the physical
sciences stem from:
 observing the sky and nature
 finding repeatable patterns
 seeking natural explanations for these patterns
 Understanding and explaining motions
observed in sky led to geometric models for the
the universe.
 These models, in turn, motivated the
development of the physical sciences: required to
explain this geometry.
 Ultimately, this led to an understanding of how
stars and planets form.
The development of Astronomy as a Science
 Prehistory - development of myths to explain natural
phenomena - no physical model
 Later, many threads of physical models were developed,
most were lost
 We owe the origins of the physical sciences to the
Greeks, later threads came from many other cultures.
 Physical models are developed to explain observations
(everything starts with observations!)
Motions in the sky:
Stellarium: www.stellarium.org -- A free open source
planetarium for your computer. It shows a realistic sky
in 3D, just like what you see with the naked eye,
binoculars or a telescope.
Screenshots
from Stellarium
Planets Known in Ancient Times
 Mercury: difficult to see; always close to Sun in
sky
 Venus: very bright when visible; always close to
Sun in sky, but can be farther than Mercury
 Mars: noticeably red
 Jupiter: very bright
 Saturn: moderately bright
Q: Why are there seven days in the week?
A: There were seven objects in the sky that
moved independently of the stars.
Roman gods associated with planets
1. Saturn: Saturday
2. Sun: Sunday
3. Moon: Monday
Anglo-Saxon or Nordic analogues to Roman gods
4. Mars: Tuesday (Tiw’s day)
5. Mercury: Wednesday (Woden’s day)
6. Jupiter: Thursday (Thor’s day)
7. Venus: Friday (Freys’ day)
Patterns Observed in the sky:
(observed facts)
Celestial Sphere
Large imaginary spherical
surface centered on the
Earth.
Stars and other celestial
objects “fixed” on its
surface.
Conceptual Model, not a
physical model
The sun follows the same path around the sky (on the
celestial sphere), repeating this journey once every year.
This path is called the “Ecliptic”
Motions of the planets
 On short term (minutes, hours), planets appear to move
with the stars, east to west, making a full circuit around the
sky (meridian to meridian) in approximately one day
 On the longer timescale (days, weeks, months), planets
move slowly eastward relative to the stars: different planets
moving at different rates
Locations of planets in the sky
Mercury: always close to Sun in sky
Venus: always close to Sun in sky
 Mars: no restrictions on distance from Sun in sky
 Jupiter: no restrictions on distance from Sun in sky
 Saturn: no restrictions on distance from Sun in sky
 Planets are always
close to the “ecliptic”,
the apparent annual
path of the sun through
the sky.
Close grouping of five
planets in April 2002.
This is a pattern that
was well known to the
“ancients”
Some planets occasionally reverse their motion
relative to the stars, moving slowly westward
relative to the stars, for a few days
apparent retrograde motion
The observed motions of the stars, sun,
moon, and planets in the sky provide us
with “observed facts”
What accounts for these observed facts?
(construct a model and then test it)