Galileo invented the telescope, right? Nope. He stole the idea and then improved on it to produce an instrument far superior to anything else available at the time. With his superior instrument, he went on to make discoveries that heralded the beginnings of modern astronomy.

Telescopes of the same design as Galileo's original are still called Galilean telescopes, but there are now many other kinds, some of them quite exotic. For example, telescopes that use a spinning circular vat of liquid mercury as a mirror. As the mercury is rotated, it is forced towards the edges of the container, forming a near-perfect parabola on the surface.

Andersen provides a broad coverage of the subject. As well as describing the different types of telescope, he also gives an account of the circumstances to which they are suited, some of the key discoveries that have been made using telescopes and some of the possibilities for telescopes of the future. If you would like to set up your own telescope, there is a brief appendix outlining some of the factors you will need to consider.

The Telescope includes an account of the very clever technique of adaptive optics. To correct distortions that are created when light travels through the Earth's atmosphere, each point on the reflective surface of the telescope is shifted up or down by a small amount. Even after having read the account of how this works, it still seems a little like magic, akin to the task of unscrambling the proverbial egg.

Telescopes are not just used to look outward to the heavens. They are also mounted in airplanes and satellites and pointed back towards the Earth for surveillance purposes. These images were once only available to intelligence services and other government agencies. Now anyone can purchase them, although presumably the highest resolution images are still reserved for intelligence agencies. Alternatively, you can view images of the Earth from surveillance satellites simply by installing the software, Google Earth, on your PC.

There is, however, one great disappointment. Not with the book itself, but with its revelation that astronomers rarely look through their telescopes any more. Instead, the images are recorded electronically. In fact, astronomers often don't even need to go to an observatory, but can control their equipment remotely. For romantics like me, this seems a great loss.