In the four centuries since its invention, the telescope has transformed how humans view the universe and their place in it. But what do most of us know about telescopes themselves; their history, how they work, what they are being used for today, or what the next generation of billion-dollar telescopes will look like? In The Telescope, Geoff Andersen fills in all the details for us in an accessible, nontechnical way that will appeal to the amateur astronomer and anyone else who has been more than a little curious about this amazing instrument.

The book covers every aspect of optical telescopes: from the humblest backyard setup, to state-of-the-art observatories, to the Hubble Space Telescope and spy satellites. Chapters describe the development, design, and operation of telescopes; how observatories are sited, engineered, and built; variations such as solar and liquid-mirror telescopes; and some of the key astronomical discoveries telescopes have made possible. And there are plenty of surprises along the way. We learn, for example, that most of today's professional astronomers never even look through their own telescopes, relying instead on digital imaging, measurement, and analysis, or even remote computer control of a night-shrouded observatory on the other side of the Earth.

But, as The Telescope explains, these magnificent instruments do more than simply peer into space. They project and receive laser beams; for communicating, mapping, and making detailed observations of the Earth. They also look down at us from spy satellites, providing secret images to intelligence agencies and, increasingly, giving a curious public access to more pedestrian images.

The Telescope is the ideal introduction to a fascinating instrument that has taught us so much, but that most of us know so little about.

"As we approach the International Year of Astronomy, the four-hundredth anniversary of Galileo's turning a telescope on the heavens, Geoff Andersen has produced an interesting book on the centuries' progress in optical observations. Chapters on telescopes used for surveillance and on a series of astronomical discoveries add interest beyond discussions of the telescopes themselves." Jay M. Pasachoff, Field Memorial Professor of Astronomy, Williams Colleg

"This book covers both the science of astronomy and the telescope technology that underlies astronomical discoveries. This balance enhances our appreciation of telescopes as engineering marvels, and it increases our understanding of what the operators of these instruments are trying to accomplish." Richard Kron, University of Chicago

"The Telescope is an extensive and thorough look at the telescope in all its modern variants, and the only book like it that I know of. I enjoyed reading it, and I'm sure that many others will too." Robert J. Vanderbei, Princeton University

Geoff Andersen is a research physicist at the United States Air Force Academy, where he studies telescope and microscope design, holography, and remote sensing. He has worked on projects funded by the U.S. Air Force and NASA.

Preface 9

Chapter 1: The naked-eye universe 13

Chapter 2: The development of the telescope 25

Chapter 3: How a telescope works 37

Imaging

Refracting telescopes

Reflecting telescopes

Chapter 4: The perfect telescope 44

Diffraction and the perfect image

Resolution limit

Chapter 5: When good telescopes go bad 53

Aberrations

Field of view

Air turbulence

Chapter 6: Analysing the light 66

Imaging devices--the camera

Spectroscopy

Photometry

Polarimetry

Chapter 7: Interferometry 80

Interference--how light waves combine

Michelson interferometer

Michelson stellar interferometer

Imaging interferometry

Nulling interferometry

Chapter 8: So you want to build an observatory? 95

Making a mirror

Site selection

Mechanical engineering

Chapter 9: The Hubble Space Telescope 109

Chapter 10: Advanced telescope techniques 125

Lightweighting

Active optics

Segmented primaries

Adaptive optics

Laser guide stars

Chapter 11: Laser communications and remote sensing 140

Laser communications

Lidar

Chapter 12: Surveillance 149

Airborne surveillance

Space-based surveillance

Other surveillance methods

Laser weapons

Chapter 13: Non-traditional observatories 162

Liquid mirror telescopes

Solar telescopes

Seeing the invisible

Gravitational wave observatories

Chapter 14: Key discoveries 181

The Solar System and Pluto

Comet Halley

The first exo-solar planet

Milky Way black hole

Hubble Ultra-Deep Field

Hoag's Object

Chapter 15: Future telescopes 197

Wide-field wonders

Another pale blue dot

The big boys

One last word 217

Appendix A: Some mathematical basics 220

Appendix B: Electromagnetic radiation 226

Appendix C: Getting your own telescope 233

Notes 236

Bibliography 240

Index 243