Greek philosophers,
the mysteries of the Egyptian sun-god, and the observations of the
ancient Chaldeans, the rich and varied traditions of astronomy stretch
far away into a shadowy past. All peoples, in the first stirrings
of their intellectual youth, drawn by the nightly splendor of the
skies and the ceaseless motions of the planets, have set up some
system of the heavens, in which the sense of wonder and the desire
for knowledge were no less concerned than the practical necessities
of life. The measurement of time and the needs of navigation have
always stimulated astronomical research, but the intellectual demand
has been keen from the first. Hipparchus and the Greek astronomers
of the Alexandrian school, shaking off the vagaries of magic and
divination, placed astronomy on a scientific basis, though the
reaction of the Middle Ages caused even such a great astronomer
as Tycho Brahe himself to revert for a time to the practice of
astrology.

EARLY INSTRUMENTS

The transparent sky of Egypt, rarely obscured by clouds, greatly
favored Ptolemy's observations. Here was prepared his great star
catalogue, based upon the earlier observations of Hipparchus, and
destined to remain alone in its field for more than twelve centuries,
until Ulugh Bey, Prince of Samarcand, repeated the work of his
Greek predecessor. Throughout this period the stars were looked
upon mainly as points of reference for the observation of planetary
motions, and the instruments of observation underwent little change.
The astrolabe, which consists of a circle divided into degrees,
with a rotating diametral arm for sighting purposes, embodies their
essential principle. In its simple form, the astrolabe was suspended
in a vertical plane, and the stars were observed by bringing the
sights on the movable diameter to bear upon them. Their altitude
was then read off on the circle. Ultimately, the circle of the
astrolabe, mounted with one of its diameters parallel to the earth's
axis, became the armillary sphere, the precursor of our modern
equatorial telescope. Great stone quadrants fixed in the meridian
were also employed from very early times. Out of such furnishings,
little modified by the lapse of centuries, was provided the elaborate
instrumental equipment of Uranibourg, the great observatory built
by Tycho Brahe on the Danish island of Huen in 1576. In this "City
of the Heavens," still dependent solely upon the unaided eye as a
collector of starlight,