Ch.1 - Science and the Universe: A Brief Tour1.1 The 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.1.2 The Nature of Sciencea hypothesis must be a proposed explanation that can betested. The most straightforwardapproach to such testing in science is to perform an experiment.If the experiment is conducted properly, its results either will agree with the predictionsof the hypothesis or they will contradict it.If the experimental result is truly inconsistent with the hypothesis, a scientist must discardthe hypothesis and try to develop an alternative.If the experimental result agrees with predictions, this does not necessarily prove that thehypothesis is absolutely correct; perhaps later experiments will contradict crucial parts ofthe hypothesis. But, the more experiments that agree with the hypothesis, the more likelywe are to accept the hypothesis as a useful description of nature.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.Much of astronomy is also ahistoricalscience—meaning that what we observe hasalready happened in the universe and we can do nothing to change it.1.3 The Laws of NatureOver centuries scientists have extracted variousscientific lawsfrom countlessobservations, hypotheses, and experiments. These scientific laws are, in a sense, the“rules” of the game that nature plays.One remarkable discovery about nature is that the same laws apply everywhere in theuniverse. The rules that determine the motion of stars so far away that your eye cannotsee them are the same laws that determine the arc of a baseball after a batter has hit it outof the park.The consistency of the laws of nature gives us enormous power to understand distantobjects without traveling to them and learning the local laws.In the same way, if every region of a country had completely different laws, it would bevery difficult to carry out commerce or even to understand the behavior of people in thosedifferent regions. A consistent set of laws, though, allows us to apply what we learn orpractice in one state to any other state.1.4 Numbers in AstronomyIn astronomy we deal with distances on a scale you may never have thought about before,with numbers larger than any you may have encountered.We use a system for writing large and small numbers calledscientific notation(orsometimespowers-of-ten notation).This system is very appealing because it eliminates the many zeros that can seemoverwhelming to the reader. In scientific notation, if you want to write a number such as
500,000,000, you express it as 5 × 108. The small raised number after the 10, called anexponent, keeps track of the number of places we had to move the decimal point to theleft to convert 500,000,000 to 5.