Overview

The unaided human eye can see individual objects as small as a few tens of microns, can detect single photons (when dark-adapted), and can see objects millions of light-years away in space. Our fingertips can feel differences in texture resulting from features less than a thousandth of an inch high, and our other senses can detect similarly small differences in molecular concentrations (taste and smell) and vibration (hearing). Yet, our eyes are poor compared to a hawk's, we cannot hear or smell as well as most dogs, and we cannot begin to duplicate a salmon's ability to taste the waters of its home stream. In order to explore and understand our world and universe, we must extend our senses further still. So we have learned to make telescopes that can see nearly to the beginning...