In the years between 1800 and the end of the twentieth century, astronomy was fundamentally transformed. That which had been at heart a science of position, in which astronomers strove to say where an object is, not what it is, became in many ways a vastly more wide-ranging and large-scale enterprise in terms of the questions asked of nature, the number of astronomers it engaged, the level of public and private support it enjoyed, and the size and sophistication of the instruments employed, as well as the remarkable extension of observations beyond the narrow window of optical wavelengths.

The focus of this chapter is on those changes in observational astronomy that comprised central elements in this remaking of astronomy between 1800 and 2000: the reform of positional astronomy in the early nineteenth century, the rise of astrophysics (although little attention is devoted to the study of the Sun, as that is discussed elsewhere in this volume), and the ways in which shifting forms of patronage provided new opportunities for state-of-the-art instruments. In all of these areas, the history of the telescope, the key instrument in observational astronomy in the last four centuries, will be key. We shall also see that the improvement of telescopes was often not tied to answering particular theoretical questions, but was rather seen as a worthy goal in itself that would, in turn, lead to novel results. It should be noted, too, that we are concerned with astronomy in the Western world at the cutting edge of research. I shall therefore not address very interesting questions about the development of instruments for use primarily in demonstrations (e.g., planetaria) or employed chiefly for recreational uses.