Astronomy occupies a rather unique position among the natural sciences. While physics, chemistry, and the biological sciences form the foundation of the extraordinary material development of our day, astronomy, in the eyes of most people, is of little practical value. What benefit could we derive from knowing whether a star lies a hundred or a thousand billion miles from the Sun, or from understanding how the stellar bodies have evolved in the course of billions of years? And yet astronomy has not been as futile as is commonly imagined, neither is it useless at the present time. This science is still of the greatest importance to common life by fixing our standards of time and, before the introduction of the compass, was invaluable also to navigation, which art, moreover, depends now upon astronomy for determination of geographical position on the open sea. Observations for these purposes, however, are of such a simple nature, that they hardly fall under the astronomical science proper, but rather under the applied sciences. They have entered into daily life much as, in commerce, the determination of the weight of a body is not considered as belonging to the science of physics, although it depends on the use of a physical instrument, the scale. But we must not forget that what we now consider so commonplace that it entirely has lost the grand aspect of science, once was the goal of groping scientific endeavour. All natural science has grown out of the needs of practical life. Geometry is probably even older than astronomy. The name means: to measure land, and the oldest geometry was, accordingly, devoted to the measurement of distances on the Earth and later to the determination of the area of land-holdings. This extremely important practical application of geometry is of such a simple nature that it is not mentioned in modern mathematical science, to which geometry belongs. In this manner, the original theses of all our natural sciences have become the possession of the public to such a degree that they are looked upon as self-evident. This is the case also with those parts of astronomy which, because of their practical importance at the outset, gave rise to the science itself.