Zoom in on the red giants and Red Peril

Galileo Galilei first looked at the sky through a telescope in 1609, so 2009 will be the 400th anniversary of mankind's first enhanced view of the universe. As a result, Unesco has named 2009 the International Year of Astronomy, embracing everything from television programmes to political campaigns against light pollution.

In addition, there is bound to be plenty to read, with a slew of books on Galileo, as well as the telescope and everything it has helped us discover.

Geoff Andersen's book is one of the first to make the connection to Galileo's anniversary, and it sets a high standard. The author is a physicist with the US Air Force and an expert on optics. He can write, and has opinions that will infuriate academic astronomers. In contrast to their endless moans about money, he says on his first page that "most countries spend an extraordinary proportion of public funds on astronomy", not least on big telescopes that cost $1 per second to run.

Andersen begins with a canter through the achievements of Galileo and of others, such as Newton, who developed new telescopes as well as new theories of light. Along the way, he shows how uncannily accurate Galileo was as an observer (unlike Newton, who preferred to devote himself to theory), and explains what determines the performance of an optical telescope.

Moving into the modern day, Andersen makes clear just how extraordinary a technology telescope-building is. A modern 10m telescope mirror is so flat that if it were scaled up to the size of Australia, the resulting landmass would have no hill bigger than a golf ball. And it takes pictures that need 250 million pixels to record, about 30 times as much data as an image from a normal digital camera.

The book is at its best when discussing modern telescopes, especially the use of computer technology to remove the distorting effects of atmospheric turbulence from the images they record.

This method was developed in secret during the Cold War to help America spy on its Communist rivals, and released for civilian use once the Red Peril had abated.

This is Andersen's own field, and he recalls memorably his first realisation that the method would allow stars that had never been seen before to be "resolved". After an astronomer explained it, he says: "I began to see how you could get addicted to this stuff."

Not everything Andersen writes is compelling. A chapter on recent astronomical discoveries, which covers material others have dealt with more interestingly, should have been omitted. He includes a chapter on unconventional telescopes that does not touch upon radio or neutrino telescopes but does look at gravity wave detectors, a choice that is never explained. But these are rare lapses.

The telescope's capacity to show us faraway things as if they were nearby has altered our understanding of the universe. But it has also changed other human activities, especially warfare and spying, because a telescope does not mind whether it points towards the Earth or away from it. This is a facet that Andersen explores in an excellent chapter on aerial and satellite espionage.

Scientific and practical uses of the telescope are also converging. Telescope systems designed to detect nearby asteroids that might hit the Earth can also spot objects in the Earth's orbit only a few centimetres across, so they have a vital role in making space flight safer.

Andersen's final chapter shows that even after 400 years, the telescope still has new things to show us. It may soon be possible to produce images and even crude maps of the earthlike planets of other stars.

One such, called OWL for the Overwhelmingly Large Telescope, would allegedly gather more light than every previous telescope put together. This is billion dollar technology, so the prodigious sums of cash Andersen mentions will go on growing deep into the telescope's fifth century.

Martin Ince is contributing editor, The Times Higher .