An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

INTRODUCTION TO ASTRONOMY.
PRELIMINARY OBSERVATIONS.
1. ASTRONOMY is that science which treats of the heavenly
bodies.
More particularly, its object is to teach what is known
respecting the Sun, Moon, Planets, Comets, and Fixed Stars;
and also to explain the methods by which this knowledge i;
acquired. Astronomy is sometimes divided into Descriptive,
Physical, and Practical. Descriptive Astronomy respects
facts; Physical Astronomy, causes; Practical Astronomy,
the means of investigating the facts, whether by instruments,
or by calculation. It is the province of Descriptive Astron
omy to observe, classify, and record all the phenomena of the
heavenly bodies, wheher pertaining to those bodies individually, or resulting from their motions and mutual relations. It
is the part of Physical Astronomy to explain the causes of
these phenomena, by investigating and applying the general
laws on which they depend; especially by tracing out all the
consequences of the law of universal gravitation. Practical
Astronomy lends its aid to both the other departments.
2. Astronomy is the most ancient of all the sciences. At a
period of very high antiquity, it was cultivated in Egypt, in
Chaldea, in China, and in India. Such knowledge of the
heavenly bodies as could be acquired by close and long-continued observation, without the aid of instruments, was diligently amassed; and tables of the celestial motions were
constructed, which could be used in predicting eclipses, and
other astronomical phenomena.
About 500 years before the Christian era, Pythcagoras, of
Greece, taught astronomy at the celebrated school at Crotona,
and exhibited more correct views of the nature of the celestial
motions than were entertained by any other astronomer of the
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