Introduction

The systems that extract information from faint signals about distant celestial bodies are the source of essentially all our astronomical knowledge. Telescopes collect and concentrate the radiation, and the instruments at their foci analyze one or more properties of the radiation. The systems used for the various frequency bands (e.g., radio, optical, and x-ray) differ dramatically from one another.

The faint signals must compete with background noise from the cosmos, the atmosphere, the earth's surface, and the detectors themselves. These noise sources differ with the frequency of the radiation. Advances in astronomy often follow from improved rejection of noise so that fainter signals can be detected. For example, improved focusing yields a smaller spot on the image plane (film or CCD), and the signal need only compete with the smaller amount of instrument noise occurring at this smaller region.

In this chapter, we present some characteristics of telescopes including their focusing properties. The diffraction phenomenon that can limit the resolution of telescopes is described. Current efforts to develop systems to remove the blurring due to the atmosphere are also discussed. In the following chapter we describe detectors that are placed at the foci of the telescopes.

Telescopes Mastery

Telescopes Mastery

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