POPULAR SCIENCE I A Popular History of Astronomy Biman Basu Popular Science COSMIC VISTAS A Popular History of Astronomy BIMAN BASU NATIONAL BOOK TRUST, INDIA ISBN 81-237-3942-7 First Edition 2002 (Saka 1924) © Biman Basu, 2002 Rs 65.00 Published by the Director, National Book Trust, India A-5 Green Park, New Delhi 110 016 Contents Acknowledgemen ts vii Preface ix 1. In the Beginning 1 2. Patterns in the Stars 7 3. Vedic Concepts 15 4. Earth at the Centre 21 5. Place of the Sun 28 6. Planetary Paths 36 7. Beyond the Eye 44 8. Newton's Genius 53 9. Einstein's Universe 63 10. Amazing Reflectors 71 11. The Radio Sky 80 12. View from Space 93 13. Planetary Worlds 105 14. Measuring the Cosmos 115 The Nakshatras 125 Recommended Reading 127 Index 129 Acknowledgements My interest in astronomy was kindled in my childhood when I watched with awe the star-filled night sky lying in a cot on the lawns of our house during the summer months. In sub- sequent years, I was inspired by the writings of eminent writers like Patrick Moore and Isaac Asimov. Although I never studied astronomy formally, my interest in the sub- ject grew with age and I began enjoying sky watching more and more. I still remember the thrill of watching the famous Halley's comet in the early hours of a March day in 1986 and the glorious sight of the Hale-Bopp comet in 1997. As I read more and more about the new developments taking place in observational astronomy, I was impressed by the enormous range of information available. But, sadly, reports of most of the breathtaking developments in as- tronomy remain hidden in research journals or in scattered articles published in popular astronomy journals. I decided to bring together all the exciting stories available on astronomical techniques and the remarkable discoveries made with the new techniques in a popular science book. The National Book Trust, India, helped me by agreeing to publish the book. I am grateful to them for the gesture. One person who has constantly encouraged me in my astronomical forays including writing this book is the former Director of Positional Astronomy Centre, Kolkata, Prof. Amalendu Bandyopadhyay. I am deeply indebted to him for going through the original manuscript and making viii COSMIC VISTAS valuable suggestions for improvement, which have helped me in bringing the text into its final form. I am also indebted to all the authors whose books and writings have been of invaluable help in checking facts and figures for the book. New Delhi BIMAN BASU Preface We all become familiar with the sky above right from our childhood days. We see the daily journey of the Sun across the sky the waxing and waning of the Moon and the star- filled night sky. But in my childhood days we hardly ever gave a thought to what these celestial objects were or why they behaved or moved the way we saw them in the sky We gradually learnt about them as we grew up. Today, how- ever, things have changed. Children know a lot about the celestial objects thanks to the discoveries made by scientists over several centuries. The story of their discoveries has all the elements of a detective thriller. The exploration of space during the past four decades has further changed the sce- nario, revealing the solar system and the Earth's cosmic neighbourhood like never before. To our distant ancestors, the Sun, Earth, Moon, plan- ets and the stars made up the entire universe, with our Earth at the centre of it. Our ancestors believed that all the celes- tial bodies visible to the unaided eye—the Sun, Moon, five planets and the stars—move around the Earth in very com- plex paths. The ancient people did not even know what the stars and planets really were or how far they were from us. There is, however, evidence that tells us that Vedic In- dians, who probably lived more than 6,000 years ago, had considerable knowledge of astronomy. We find evidence of astronomical observations as early as 4,000 B.C. in the verses of the Rig Veda. But the oldest astronomical text in India is the Vedanga Ji/otisha, which is dated about 1,400 B.C. viii COSMIC VISTAS Gradually, with advances in science and technology, as telescopes and other observation tools were invented to study the universe, the real nature and shape of the uni- verse gradually unfolded. With the help of astronomical records of hundreds of years, the Polish astronomer Nicolaus Copernicus in the 16th century established the Sun at the centre of the planetary family we call the 'solar system'. Later work by Johannes Kepler and Isaac Newton explained the way the planets moved around the Sun, thus solving a long-standing riddle of planetary motions. But more than that, these developments shifted the position of the Earth from being the hub of the universe to that of an insignifi- cant member of the solar family. The invention of the telescope in early 17th century brought in a revolution of sorts. For the first time, a single technological development radically changed all our ideas about the universe. It revealed the real nature of the celes- tial bodies like the Moon, the planets, and the Milky Way— the galaxy of which the Sun and its planetary family is a part. As more powerful telescopes came, distant galaxies were discovered which extended the limits of our universe manifold. The vastness of the universe gradually started unfolding. Astronomers discovered that the stars that we see as tiny specks of light in the night sky are actually suns, many of them hundreds or thousands of times larger than our Sun. In fact, it turned out that our Sun is a very ordi- nary and medium-sized star the like of which there are bil- lions and billions in the universe, making up billions of gal- axies like our Milky Way galaxy. As techniques of astronomical observation were fur- ther refined and newer tools were put to use, giant clouds of gas and dust were discovered in space where stars were being born. Astronomers also recorded the dying moments of giant stars that end up with flashes of brilliance so bright that sometimes they can be seen in broad daylight. Stars were found to be mortal, like us humans. They were born from giant clouds of gas and dust, lived till old age and