Observing Photons in Space

This first chapter of the book “Observing Photons in Space” serves to illustrate the rewards of observing photons in space, to state our aims, and to introduce the structure and the conventions used. The title of the book reflects the history of space astronomy: it started at the high-energy end of the electromagnetic spectrum, where the photon aspect of the radiation dominates. Nevertheless, both the wave and the photon aspects of this radiation will be considered extensively. In this first chapter we also describe the arduous efforts that were needed before observations from pointed, stable platforms, lifted by rockets above the Earth’s atmosphere, became the matter of course they seem to be today. This exemplifies the direct link between technical effort — including proper design, construction, testing and calibration — and some of the early fundamental insights gained from space observations. We further report in some detail the pioneering work of the early space astronomers, who started with the study of gamma- and X-rays as well as ultraviolet photons. We also show how efforts to observe from space platforms in the visible, infrared, sub-millimetre and microwave domains developed and led to today’s emphasis on observations at long wavelengths.