Page:The Moon (Pickering).djvu/119

 CHAPTER XI

earliest recorded observations of the Moon relate to eclipses. The first of those that has come down to us was made by the Chinese about 2158 B. C. But even at this early date the prediction of an eclipse was possible, as we know from the sad fate of the royal astronomers, Hi and Ho, who, we are informed, owing to their indulgence in strong drink and riotous living, failed to predict this particular eclipse and were therefore summarily executed. Recently some very interesting astronomical observations have been discovered at Nippur, made by the ancient Babylonians before the time of Abraham, about 2000 B. C. It is certain that they knew that the Earth was spherical, and they also were familiar with the Saros, which is a period of a little over eighteen years, and was used by the ancients for the prediction of eclipses. Aristotle (384–322 B. C.) showed that the Moon was spherical, and was nearer to us than Mars, since he observed an occultation of the latter by the former. Aristarchus (320–250 B. C.) believed that the Svm was the centre of our system. He measured the distance and diameter of the Moon. The former he determined to be fifty-six times the radius of the Earth—a result that was very nearly correct. The latter strangely enough he placed at about two degrees—a figure nearly four times too large. Hipparchus (190–120 B. C.) was the greatest of these early astronomers. He determined the shape and inclination of the Moon's orbit, and also its distance and diameter, with considerable accuracy. He was followed by Ptolemy (100–170 A. D.), who discovered the chief irregularity in the Moon's orbit, which is caused by the action of the Sun, and is known as the evection.

From the days of Ptolemy no important discoveries pertaining to the Moon were made until Tycho Brahe (1546–1601). This distinguished astronomer, by means of improved instruments, greatly increased the accuracy of our knowledge of the Moon's orbit, and discovered the two other large inequalities of its motions—the variation and annual equation.

By means of the telescope Galileo (16 10) greatly increased our knowledge of the surface of our satellite, for he substituted facts for theories. He recognised that it was largely a mountainous region, and he constructed the first map of its surface. He 83