Seeing in the Dark: How Backyard Stargazers Are Probing Deep Space and Guarding Earth from Interplanetary Peril
Timothy Ferris is a serious amateur astronomer. He spends a substantial amount of his time and money roaming around at night among planets and stars and galaxies. He owns a place called Rocky Hill Observatory in California where he can stargaze to his heart’s content through telescopes of modest size and excellent quality. He belongs to the international community of observers who are linked by the Internet as well as by the shared sky in which they are at home. Serious amateur astronomers, unless they are retired or independently wealthy, must have a day job to support their nocturnal addiction. Ferris has a day job as a writer of books explaining science to the general public. He has written many books which are widely read and have effectively reduced the level of scientific illiteracy of the American population.
This book is similar to the others in some respects and different in others. Like his previous books, it is factually accurate, it contains a wealth of information about the universe we live in, and it makes the information easily digestible by seasoning it with good stories. Unlike his other books, it is a love story, describing how Ferris fell in love with astronomy at the age of nine and how this passion has enriched his life ever since. But he does not write much about himself. The book is mainly a portrait gallery of the diverse and colorful characters who have shared his passion, with a description of the contributions that they have made to the science of astronomy.
Ferris has sought out his amateur astronomical colleagues, visited them in their homes and observatories, listened to their life stories, and watched them at work. One of these colleagues is Patrick Moore, who has also supported himself by writing popular science books in the daytime while exploring the sky at night. Ferris visited him in the English village of Selsey where he lives and works. Many years ago, before any human beings or human instruments had surveyed the back side of the moon from space, Moore was observing the moon systematically with his small telescope at Selsey.
The moon normally keeps a fixed orientation as it revolves around the Earth, so that only the front side is visible. But it wobbles slightly in its orbit, so that occasionally some regions that are normally invisible can be seen at the edge of the visible face, extremely foreshortened and inconspicuous. Moore was studying these normally invisible regions at a moment when the moon’s wobble was at a maximum, and discovered Mare Orientale, the biggest and most beautiful impact crater on the moon. Moore gave it the name Mare Orientale, Eastern Sea, because it is hidden behind the eastern edge of the moon and because it is a dark circular region similar to the dark regions on the front side of the moon which the amateur astronomer Johannes Hevelius called seas when he mapped them in 1647.
Hevelius was a brewer in Danzig who made the first accurate map of the moon. Even at times of maximum wobble, only a small part of Mare Orientale can be seen from the Earth. Only an observer with long experience and deep knowledge of lunar topography could have recognized it in the fragmentary view of the moon’s edge that Moore could see from Selsey. Professional astronomers do not have such experience or such knowledge. Only an amateur could have discovered Mare Orientale, because only an amateur has the time and the motivation to study a single region of the moon with single-minded dedication.
Patrick Moore is one of many examples illustrating the main theme of Ferris’s book. The theme is the importance of amateurs in the exploration of the universe, not only in past centuries but also today. Patrick Moore was an old-fashioned amateur when he discovered Mare Orientale, observing the moon laboriously with his eye at the telescope, drawing maps of his observations with pencil and paper. Amateurs today observe the sky with digital electronic cameras, recording the images with personal computers using commercial software. The role of amateurs has become more important in the last twenty years, because of the advent of cheap mass-produced electronic cameras, computers, and software. Serious amateurs today can afford to own equipment that few professional observatories could afford twenty years ago. Personal computers are used not only to record data but to communicate rapidly with other observers and to coordinate observations all over the world.
There are many areas of research that only professional astronomers can pursue, studying faint objects far away in the depths of space, using large telescopes that cost hundreds of millions of dollars to build and operate. Only professionals can reach halfway back to the beginning of time, to explore the early universe as it was when galaxies were young and the oldest stars were being born. Only professionals have access to telescopes in space that can detect the X-rays emitted by matter heated to extreme temperatures as it falls into black holes.
But there are other areas of research in which a network of well-equipped and well-coordinated amateurs can do at least as well as the professionals. Amateurs have two great advantages, the ability to survey large areas of sky repeatedly and the ability to sustain observations over long periods of time. As a result of these advantages, amateurs are frequently first to discover unpredictable events such as storms in the atmospheres of planets and catastrophic explosions of stars. They compete with professionals in discovering transient objects such as comets and asteroids. It often happens that an amateur makes a discovery which a professional follows up with more detailed observation or theoretical analysis, and the results are then published in a professional journal with the amateur and the professional as coauthors.
On Palomar Mountain in California there are two famous telescopes, the huge 200-inch and the little 18-inch. The 200-inch was for many years the largest in the world, exploring the far reaches of the universe with unequaled sensitivity. The 18-inch was on the mountain before the 200-inch and made equally important discoveries. It was the brainchild of the German amateur astronomer Bernhardt Schmidt. Schmidt was a professional optician who made a living by grinding lenses and mirrors. He worked as an unpaid guest at the university observatory in Hamburg. In 1929 he invented a new design for a telescope that produced sharply focused photographic images over a wide field of view. He built and installed the first Schmidt telescope at Hamburg. The Schmidt telescope made it possible for the first time to photograph large areas of sky rapidly. Compared with previously existing telescopes, the Schmidt could photograph about a hundred times more area every night.
The 18-inch at Palomar was the second Schmidt telescope to be built and the first to be used in a mountaintop observatory with good astronomical seeing. Fritz Zwicky, a Swiss professional astronomer, understood the potential of Schmidt’s invention and installed the 18-inch on the mountain in 1935. He used it to do the first rapid photographic sky survey, photographing large areas of sky every night and mapping the positions of hundreds of thousands of galaxies. As a result of this survey, Zwicky made two fundamental discoveries. He found that galaxies have a universal tendency to congregate into clusters. And he found that the visible mass of the galaxies is insufficient to account for the clustering. From the observed positions and velocities of the galaxies, Zwicky calculated that the clusters must contain invisible mass that is about ten times larger than the visible mass. His discovery of the invisible mass, made with the little Schmidt telescope, opened a new chapter in the history of cosmology. Our later explorations of the cosmos have confirmed that Zwicky was right, that the dark unseen mass dominates the dynamics of the universe. Professional and amateur astronomers are using Schmidt telescopes all over the world to continue the revolution that Schmidt and Zwicky started. Schmidt himself did not live to see the triumph of his invention. When Hitler came to power in Germany in 1933, Schmidt was so disgusted that he gave up hope and quietly drank himself to death.
David Levy is an amateur astronomer in the modern style. He observes at his home in Arizona where he has three modest but well-equipped telescopes, two of them of Schmidt design. He has also visited frequently as a guest observer at the Palomar observatory in California, where he collaborates with the professionals. At Palomar he was using Zwicky’s original 18-inch telescope, which was still going strong and making important discoveries after sixty years of intensive use. His collaborators were Eugene and Carolyn Shoemaker, until Eugene’s untimely death in a car accident. Now he continues the collaboration with Carolyn alone.
The most famous event of the collaboration occurred in 1993 when Eugene was still alive. This was the discovery of the comet Shoemaker-Levy 9, which was seen in the process of tidal disruption after passing too close to the planet Jupiter. The newly discovered comet was at that moment breaking up into eighteen pieces. The pieces moved apart until they looked like a string of pearls, stretched out into a straight line, each with its own tail of gas and dust shining in the light of the distant sun. After a few days of careful observation and calculation, it became clear that the pieces of the comet were all destined to crash into Jupiter sixteen months later. This was the first time in the history of astronomy that two celestial objects were seen to collide.
At the time when Jupiter was under bombardment in July 1994, I was lucky to be a guest of the amateur astronomer Gilbert Clark in the dome occupied by a 24-inch telescope on Mount Wilson in California. Clark is a retired Navy officer who founded and directs a charitable foundation called Telescopes in Education, or TIE for short. The 24-inch telescope is on loan from the Mount Wilson Observatory to TIE and is instrumented so that it can be operated by remote control. While Clark and I were in the dome, the telescope was being operated by children in a classroom in Virginia. We could see the same images that the children were seeing, and we could hear their voices. They were deciding where to point the telescope. They looked intermittently at various deep-sky objects, galaxies, and star clusters, but always came back to Jupiter. There on the screen was Jupiter, not the familiar image of Jupiter with bland horizontal bands in its cloudy atmosphere, but a wounded Jupiter with five big black scars at the places where fragments of the comet had struck. To me the most remarkable feature of the view was that we could see Jupiter spinning. The scars made the rotation of the planet visible. Jupiter spins fast, making one revolution in nine hours, forty degrees of longitude per hour. We could see the scars moving across the face of the planet, disappearing at one edge and appearing at the other. And the children could see them too.