With the development of modern theoretical astrophysics, astronomers

With the development of modern theoretical astrophysics, astronomers are able to explain data collected by early observers and to amass data about previously unknown phenomena in extragalactic optical astronomy. Despite our lack of understanding of these new phenomena, the data is being used for a variety of purposes. In certain cases it is possible, by application of known physical laws, to make theoretical predictions that are subject to observational tests. The prediction of neutron stars is a classic example of the use of this type of theory for purposes of prediction. Another is to be found in the field of cosmology.

Much of the current activity in extragalactic astronomy is directed towards deciding which if any, of the theoretical models of the universe is the most accurate. Starting from Einstein’s Theory, which proposed a radically different approach – the steady-state theory of the universe. This cosmology dispensed with the idea of a primordial singularity demanded by Hubble’s theory and substituted the concept of continuous creation of matter, which would maintain approximately constant mean density. It is largely within the context of these two theoretical models that observational work has found both its inspiration and its justification. Theoretical predictions of the type outlined above are of particular importance to astronomy, which is an observational rather than an experimental science. Predictive theory that is concerned with the consequences of physical laws is thus immensely productive in an astronomical context and can lead to lively interaction with the observational aspects of the subject.

It would, however, be unfair to suggest that theory usually plays such a guiding role in astronomical endeavor. Indeed, more often, theories are motivated by discoveries. As a result the second major role of theory in astronomy is that of interpretation. In the field of stellar evolution, for example, the general features of the Hertzprung-Russell diagram (essentially a plot of luminosity versus temperature) had been known for many years before a theoretical interpretation in terms of nuclear processing in unmixed stars could be given. This quantitative explanation opened the way to the development of a method for using the results of stellar-evolution calculations to provide us with quantitative information about stars. In principle, this method can be used to determine the approximate stellar abundances of the chemical elements, stellar masses, and hence stellar ages. Indeed, stellar-evolution theory provides us with the only widely applicable method of dating stellar systems.

1. The primary purpose of the passage is to

A) Elucidate ways in which astronomy differs from other sciences.
B) Discuss the roles of observation and theory in astronomy.
C) Present two conflicting views of the origin of the universe.
D) Demonstrate how the laws of physics apply to astronomy.
E) Explain the importance of stellar-evolution theory.


2. Which of the following represents a methodological handicap in the field of astronomy?

A) The difficulty of formulating predictive theories.
B) The impossibility of evaluating data collected by early observers.
C) The difficulty of correlating observed data with theoretical predictions.
D) The theoretical problem of reconciling the laws of astronomy with known laws of physics.
E) The difficulty of testing hypotheses through experimentation.


3. It can be inferred that the author considers predictive theory to be important in astronomy because it

A) Can be easily verified on the basis of objective data.
B) May provide a framework for further astronomical observation.
C) May result in confirmation of known physical laws.
D) Confirms the validity of data on the origins of the universe.
E) Often contributes to the advancement of other sciences.


4. The passage would be most likely to appear in which of the following.

A) A specialized monograph on astrophysics and its methods.
B) A newspaper article discussing cosmology.
C) A popular discussion of basic physical laws.
D) A theoretical essay on chemical elements in the universe.
E) A popular article on techniques of optical observation.


5. With which of the following statements concerning both the predictive and the interpretive roles of astronomical theory would the author be most likely to agree?

A) Both stimulate new research and provide a background against which astrophysical phenomena can be understood.
B) Both focus on discovering which model of the universe is correct.
C) Both are useful for validating information collected by observation as well as for testing the application of known physical laws.
D) Both have contributed about equally to every advance in astronomy and physics.
E) Both have as their primary objectives the formulation of new hypotheses.


6. The author uses the example of the Hertzsprung-Russell diagram in order to illustrate which of the following assertions?

A) Theory plays an important role in providing explanations for existing data.
B) Qualitative theory sometimes leads to the collection of quantitative information.
C) Quantitative data can provide an explanation for nuclear processing in unmixed stars.
D) There is a mathematical relationship between luminosity and temperature in stars.
E) Quantitative methods can be used to determine the mass and age of any star.


7. The author regards theoretical speculation on the origins of the universe with

A) Mild skepticism.
B) Restrained enthusiasm
C) Anxious concern.
D) Cool indifference.
E) Objective detachment.