Institution(s): 1. retired
The term "revolution" in scientific contexts usually refers either to the beginnings of modern western science in the sixteenth and seventeenth centuries, or to the two great revolutions of early twentieth century physics. Comparison of what was known at the beginning of the nineteenth century with what was known at the end, however, shows that century to have been one of transformation in astronomy, and in the other sciences, that amounts to "revolution". Astronomers in 1800 knew neither the nature of the Sun nor the distances of the stars. Developments in instrumentation enabled the first determinations of stellar parallax in the 1830s, and later enabled the solar prominences to be studied outside the brief momemnts of total eclipses. The development of photography and of spectroscopy led to the birth of observational astrophysics, while the greater understanding of the nature of heat and the rise of thermodynamics made possible the first attempts to investigate the theory of stellar structure. Nothing was known in 1800 of extra-galactic objects apart from some tentative identifcations by William Herschel but, by the end of the century, the discovery of the spiral structure of some nebulae had led some to believe that these were the "island universes" about which Kant had speculated. Of course, astrophysics and cosmology would be much further developed in the twentieth century and those of us whose careers spanned the second half of that century look back on it as a "golden age" for astronomy; but the nineteenth century was undoubtedly a time of rapid transformation and can be reasonably described as as one of the periods of revolution in astronomy.