The Labyrinths of Heaven

Abstract

Astronomy became a popular subject of study and interest with the general public in the eighteenth century. Indeed, scientific lecturing could be a successful career for enterprising amateurs who would advertise their courses, hire lecture rooms and charge fees. Lectures on astronomy were illustrated by means of models of various kinds. The basic equipment was a pair of globes – the familiar terrestrial globe as still used showing the territories of the Earth, and a celestial one, showing the principal stars in their constellations. Each globe had its engraved coordinates – the terrestrial one with its circles of longitude and parallels of latitude; the celestial one with the equivalent set of coordinates, right ascension and declination. Mounted in a stand, each globe was rotatable around its polar axis which was tilted at an angle of 23. 4^∘ to the horizontal, indicating the inclination of the equators of the Earth and the celestial sphere to the ecliptic, the plane of the Earth’s path around the Sun. Pairs of beautiful globes – today much sought-after artistic items – were part of the furniture of well appointed houses. From the terrestrial globe one could discover, in the simplest example, the time difference between geographical locations. The celestial globe could be used to indicate the position of the Sun in the zodiac at various times of the year. With further instruction, more complicated problems relating to the appearance of the heavens could be solved. “The use of the globes” came to be a standard element in geography lessons in schools. Another topic of instruction was “dialling”, or the art of making faces of sundials. Ladies, who might not consider using a telescope in the cold outdoors, could learn about the heavens in the comfort of their drawing-rooms from a celestial globe or from suitable books that explained the movements of the heavens. The more studious among them might even attend – or be permitted to attend – public scientific lectures.

The working of the solar system was illustrated by the orrery (Fig. 2.1), a mechanical apparatus that represented the planets in their orbits as balls moving by wheelwork in circles around a model Sun. One type of orrery showed the Earth, accompanied by its orbiting Moon, and could be used to explain the phases of the Moon and the occurrence of solar and lunar eclipses. A more elaborate and very beautiful instrument, sometimes also called a planetarium (though in modern times a planetarium has a different meaning) showed the known planets of the solar system, with their respective moons, all capable of performing their assigned movements by the turning of a handle. The entire interest was in the mechanics of the solar system. The stars, at unfathomable distances, were merely a backdrop against which the movements of the Sun, Moon and planets were observed. Astronomy, in the sense of a knowledge of the nature of stars or of the wider universe, played no part.