Exploring Stars and Books
 

T
 

LLOYD MOTZ
 

j/" If ^ HE use of source material in astronomy presents interest¬
ing features which are not found in the other sciences
or social sciences. Of course, in so far as contemporary
source material is concerned, the astronomer, the physicist, the
chemist, and the other scientists are on the same footing; they can
do useful research only by maintaining day to day contact with
the current papers published in their fields. But the astronomer
must go further than this, for he must also review work that was
done in his field as far back as recorded observations go if he is to
obtain answers to important astronomical questions.

The reason for this is that astronomy, as an exact science, dif¬
fers from other exact sciences, such as physics, in one essential
respect; it is observational rather than experimental, and its obser¬
vational material is beyond the control of the astronomer. It is true
that the stars, the planets, the sun, the moon, and all other heavenly
bodies are the same for all observers, but events may occur in the
structure and motions of these bodies that can never be repro¬
duced. Whereas in physics one can perform precisely the same
experiment as often as may be desired, no two observations in
astronomy can be exactly alike because all the heavenly bodies
and their configurations are undergoing change, albeit very
slowly, and it is by comparing observations from year to year
that important discoveries are made. Some extremely interesting
examples of this are to be found in the astronomy source material
in the Special Collections Department of the Columbia Libraries.

The dominant figure in observational astronomy up to tlie time
of Newton was Tycho Brahe, whose amazingly accurate observa¬
tions led to the discovery of the laws of planetary motion. On a
November evening in the year  1572,  Tycho observed what

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