HISTORY OF THE TELESCOPE -

A VISUAL ESSAY

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Traditions in Astronomy

    When a telescope was first directed to the heavens by Galileo, there was already a well established tradition in astronomy, that the function of astronomers was to understand and predict the motions of the sun, moon and stars against the graph paper of their starry background. This meant that the system of stellar positions was fundamental to every task undertaken by the astronomer and developing accurate positions for the stars was therefore a primary task. After the fifteenth century, global exploration increased the value of such knowledge enormously and thereafter interest never waned as the need for accurate methods of navigation and surveying grew. National observatories were established in Greenwich, Paris and elsewhere to support the development of catalogues of precise stellar positions and later for accurate determinations of time for use in navigation. A strong relationship developed between observatory astronomers and the instrument makers who provided increasingly accurate instruments to support this tradition of precise stellar position measurements. In the Precision Tradition, great emphasis was placed on building instruments with highly stable mountings and finely divided circles with which to measure positions of stars and other celestial objects.

    Galileo, on the other hand, used his telescopes to observe the physical nature of celestial objects. In the process he discovered that by increasing the size and magnifying power of his telescopes he could resolve our Milky Way into thousands of hitherto unsuspected stars, see features on the surface of the moon and sun that were previously considered to be unblemished spheres, follow the changing phases of Venus and discovered that the planet Jupiter was accompanied by four satellites. The exploration of the night sky thereby became a second tradition, but in contrast to the observatory based Precision Tradition, this second approach to astronomy recognized and extended Galileo's logic, larger telescopes and higher magnification were needed to discover more distant, fainter objects and examine familiar objects in greater detail. The telescope makers in the Power Tradition in astronomy relied less on the incremental improvements in fine machine work of precision instrument makers than on the combination of their own improvisations with the emerging technology of the industrial revolution. Innovative new telescopes were frequently the product of amateur astronomers who took entrepreneurial risks in their pursuit of the opportunity to discover new objects. Eventually, the larger telescopes proved their worth gathering light for astrophysical instruments and development of modern giant telescopes became the province of professional rather than amateur entrepreneurial astronomers, thus investing the Power Tradition with the same authority that had been enjoyed for centuries by the Precision Tradition.

    This visual essay on the history of the telescope is therefore a pictorial representation of the parallel evolution of these two separate traditions in astronomy. Many of the key features that emerged in each tradition will be apparent with a careful examination of the two sequences of photographs.

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