e the positions of the
celestial bodies in the sky with respect to each other; and, from
observations thus made, they constructed charts of the stars. The
earliest complete survey of this kind, of which we have a record, is the
great Catalogue of stars which was made, in the second century B.C., by
the celebrated Greek astronomer, Hipparchus, and in which he is said to
have noted down about 1080 stars.

It is unnecessary to follow in detail the tedious progress of
astronomical discovery prior to the advent of the telescope. Certain it
is that, as time went on, the measuring instruments to which we have
alluded had become greatly improved; but, had they even been perfect,
they would have been utterly inadequate to reveal those minute
displacements, from which we have learned the actual distance of the
nearest of the celestial orbs. From the early times, therefore, until
the mediaeval period of our own era, astronomy grew up upon a faulty
basis, for the earth ever seemed so much the largest body in the
universe, that it continued from century to century to be regarded as
the very centre of things.

To the Arabians is due the credit of having kept alive the study of the
stars during the dark ages of European history. They erected some fine
observatories, notably in Spain and in the neighbourhood of Bagdad.
Following them, some of the Oriental peoples embraced the science in
earnest; Ulugh Beigh, grandson of the famous Tamerlane, founding, for
instance, a great observatory at Samarcand in Central Asia. The Mongol
emperors of India also established large astronomical instruments in the
chief cities of their empire. When the revival of learning took place in
the West, the Europeans came to the front once more in science, and
rapidly forged ahead of those who had so assiduously kept alight the
lamp of knowledge through the long centuries.

The dethronement of the older theories by the Copernican system, in
which the earth was relegated to its true place, was fortunately soon
followed by an invention of immense import, the invention of the
Telescope. It is to this instrument, indeed, that we are indebted for
our knowledge of the actual scale of the celestial distances. It
penetrated the depths of space; it brought the distant orbs so near,
that men could note the detail on the planets, or measure the small
changes in their positions in the sky which resulted from the movement
of our own globe.

It was in the year 1609 that