* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Looking Deeper into Astronomy
Survey
Document related concepts
Space Interferometry Mission wikipedia , lookup
Hubble Space Telescope wikipedia , lookup
Optical telescope wikipedia , lookup
James Webb Space Telescope wikipedia , lookup
Reflecting telescope wikipedia , lookup
Allen Telescope Array wikipedia , lookup
Leibniz Institute for Astrophysics Potsdam wikipedia , lookup
CfA 1.2 m Millimeter-Wave Telescope wikipedia , lookup
Very Large Telescope wikipedia , lookup
Transcript
1-1 I Looking Deeper into Astronomy Computers in Astronomical Research f you ask the average person what astronomers do on the job, the response will likely be, “They look through telescopes.” Telescopes for visible light are indeed important tools of astronomy, and they make the universe accessible to countless amateur astronomers. Hardly any professional astronomers actually look through telescopes, however. Instead, images are recorded electronically using much the same technology as is found inside a video camera. (In Chapter 6 of Universe we will see the advantages of this technology over the human eye.) Other telescopes are sensitive to invisible forms of light such as X rays or radio waves; there is no way that one could “look through” such telescopes. Furthermore, many astronomers seldom, if ever, even go near a telescope. These researchers analyze new data or develop theories to explain the data. The only piece of hardware that is used on a daily basis by all astronomers is the computer. A number of computers of different kinds can be found at any modern observatory. Some are used to control the orientation of the telescope and to keep it pointed at the object under study; other computers may regulate the shape of the telescope optics to keep the image in the sharpest possible focus; and ordinary personal computers help astronomers keep in contact with their colleagues around the world through electronic mail. Perhaps most important, a computer records the data gathered by the telescope’s electronic detector and saves it (on magnetic media such as a hard disk) for later study. Once the stored data are returned to the astronomer’s office, which may be thousands of kilometers from the telescope, other computers are used for data analysis. Several decades ago photographic film was used to record almost all telescopic images, and extracting all of the information from such photographs was often a slow and difficult process. But when images are stored in electronic form, computers can digest those images directly and process them quickly to bring out the most subtle details. Many of the astronomical images in this book were processed in just this way. Software for this purpose is even available for personal computers and is used by many amateur astronomers who have electronic detectors on their telescopes. Besides their role in collecting and analyzing data, computers have also changed the character of much astronomical research in a fundamental way. Consider the plight of an astronomer who wants to understand why the galaxy shown in Figure 1-7 (see page 6 of Universe) has such a beautiful pattern of spiral arms. The answer must lie in the laws of physics that describe the behavior of the stars and nebulae that constitute the galaxy. Although these laws are known, the problem seems completely intractable, because the galaxy contains an astronomically large number of stars. An equally large number of intertwined equations would have to be solved to describe the motions of these stars, and a scientist with pencil and paper will not live long enough to solve them. But such problems have become tractable in recent years with the development of high-speed supercomputers. The laws of physics can be written in such a way that they can be solved by a supercomputer. In their basic form, the laws of physics are valid at every point in space and at every moment of time. But scientists seldom need to apply these laws everywhere at all times. Instead, they use points in space separated by distances that are small compared to the size of the object under study. They also use time intervals that are short compared to the duration of the process they want to examine. By programming a supercomputer with the laws of physics expressed only at these selected points and time intervals, scientists can reduce a complicated problem to a form that the machine can handle. For example, to analyze the spiral galaxy in Figure 1-7, you start with all of the stars at certain positions and moving with certain speeds. Knowing the gravitational influences that each star feels from all of the others, you can compute how each star will move over a brief time interval. (In a spiral galaxy, individual stars may take hundreds of millions of years to complete one orbit around the galaxy’s center, so a “brief” time interval may be a hundred thousand years or so.) Now you can repeat the entire t=0 t = 0.5 t = 1.0 t = 1.5 t = 2.0 t = 2.5 (After F. Hohl et al.) calculation using the data for the stars in their new positions. Step by step, you compute the motions of all of the stars within the galaxy. Modern supercomputers are ideal for performing these repetitive computations. The accompanying figure shows the result of just such a calculation using 100,000 simulated stars. The individual pictures are like frames from a movie, showing how the simulated galaxy evolves. Note that a spiral structure forms naturally, although it subsequently fades away. Much of our present-day understanding of galaxies is based on such supercomputer simulations. Using supercomputers, astronomers can simulate phenomena that might otherwise never be observed. For example, supercomputers have helped astronomers see how the Moon might have been created by a Mars-sized object striking Earth. They have revealed what happens when gas is captured and swallowed by a black hole. And they have let astronomers watch as two galaxies, consisting of thousands of stars and gas clouds, collide and interact with each other, a process that in reality takes millions of years. These are just a few examples of the essential role of the computer in modern astronomy.