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.”

● 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. The Nature of Science -- a model which survives repeated testing Theory

“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: -- 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”

 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 Motions of the planets

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 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)