1.Science and the Universe: A Brief Tour1.1The Nature of AstronomyAstronomyis defined as the study of the objects that lie beyond our planet Earth and theprocesses by which these objects interact with one another.For example,the universe made the carbon, the calcium, and the oxygen necessary toconstruct something as interesting and complicated as you.1.2The Nature of ScienceAs a concrete astronomical example, ancient astronomers constructed a model (partly fromobservations and partly from philosophical beliefs) that Earth was the center of the universe andeverything moved around it in circular orbits.As the centuries passed and improved instruments were developed for keeping track of objectsin the sky, the old model (even with a huge number of circles) could no longer explain all theobserved facts. As we will see in the chapter onObserving the Sky: The Birth of Astronomy, anew model, with the Sun at the center, fit the experimental evidence better. After a period ofphilosophical struggle, it became accepted as our view of the universe.you will find discussions of recent, and occasionally still controversial, hypotheses in astronomy.For example, the significance that the huge chunks of rock and ice that hit Earth have for life onEarth itself is still debated.while the evidence is strong that vast quantities of invisible “dark energy” make up the bulk ofthe universe, scientists have no convincing explanation for what the dark energy actually is.Resolving these issues will require difficult observations done at the forefront of our technology,and all such hypotheses need further testing before we incorporate them fully into our standardastronomical models.a hypothesis must be a proposed explanation that can betested.If the experiment is conducted properly, its results either will agree with the predictions of thehypothesis or they will contradict it. If the experimental result is truly inconsistent with thehypothesis, a scientist must discard the hypothesis and try to develop an alternative.If theexperimental result agrees with predictions, this does not necessarily prove that the hypothesisis absolutely correct; perhaps later experiments will contradict crucial parts of the hypothesis.One way to think about this is to consider a scientist who was born and lives on anisland where only black sheep live. Day after day the scientist encounters black sheeponly, so he or she hypothesizes that all sheep are black. Although every observed sheepadds confidence to the hypothesis, the scientist only has to visit the mainland andobserve one white sheep to prove the hypothesis wrong.
astronomy is sometimes called anobservationalscience; we often make our tests byobserving many samples of the kind of object we want to study and noting carefully howdifferent samples vary.