Survey ofthe UniverseClick here for textbookChapter1
Chapter 1Science and theUniverse: A Brief Tour
1.1 The Nature of Astronomy•Astronomy is the study of thesky.•Science is a progress report.•Our understanding of sciencechanges as we get new data.The Orion Nebula
1.2 The Nature of Science•Model:A simplified explanation of some natural phenomenon that can be used topredict future results. Example: The heliocentric model can be used to predict wherethe planets will be in the future.•Hypothesis:A proposed explanation that is narrowin scope and based on evidence& reason. Example: The Nebular Hypothesis says our solar systemwas formed froma collapsing cloud of gas.•Theory:a proposed explanation that is broadin scope and based on evidence &reason.•Note: A theory is not an opinion! If someone dismisses a scientific theory as“just a theory”, they don’t know what a theory is.•Example: The Nebular Theory says that planetary systems in generalare formedfrom collapsing clouds of gas.•Law:A mathematicalrule that nature sometimes (or always) obeys. Example: fromKepler’s 3rdLaw, you can compute a planet’s orbital period from its orbital radius.
Notes on terminology:Model, Hypothesis, Theory, Law•There is considerableoverlapamong the above terms.•In some cases, two or more of them are interchangeable.