Five billion years ago, at about 9:30 in the morning, a burst of photons left a faraway star, traveling in a reasonably straight line. During the long journey of this vast wave of light, out there somewhere in the Milky Way galaxy, the planet Earth was born. On Earth, from the primordial ooze evolved protozoa. During the last four million years of the journey of the photons, the planet Earth was evolving a variety of unusual species including one which we call optical engineers. So, despite the photons' long journey, during which they were pretty much unchanged, they could finally reach the inquiring eyes of astronomers like Tycho Brahe or the clever inventor Galileo.
However, after five billion years, after literally staying on the straight and narrow, heading towards the blue planet, in the last millisecond (the last darn thousandth of a second!) the photons encountered the atmosphere of planet Earth. Air, seemingly transparent, should provide a nice soft landing environment for the photons. After all, the atmosphere slows down each photon from 186,280 miles per second to about 186,230 mps. The problem arises when part of the vast wave entering the atmosphere slows down a little more than another part. Although the difference in time is only a millionth billionth of a second, the information that the wave carries is garbled. The star's precise position, velocity, type, planetary neighbors, and most recent sports scores are distorted by the atmosphere.
During the course of human history, some people worried about the problem. (Isaac Newton, for instance.) Some people ignored it. (Most everybody else.) And only in the latter half of the 20th century did anybody do anything about it. This is their story and the story of whatever it was that they did about it.
Chapter 1 is a broad overview of practically everything about adaptive optics (AO). The later chapters describe the details. This is by no means an exhaustive review of the entire field of adaptive optics. For that, refer to the articles, book chapters, and monographs listed as footnotes or at the end of each chapter. To get the most out of this book, treat it like a course. Imagine the instructor. Now imagine the instructor ignoring your questions.
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