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| Sunday, 12 June 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Space telescopes for a clearer view
Over the centuries, telescopes have grown bigger and better, the view clearer and sharper. However, once telescopes reached a size that allowed them to see quite well, astronomers faced a problem unrelated to the telescope's design. It was the Earth's atmosphere. As light passes through the atmosphere, it can be bent in unpredictable ways by warm and cool air pockets. This meant astronomers were constantly studying the skies through a shimmering field - as though they were trying to see objects through a heat haze. When we look at the stars with our naked eyes, the atmosphere makes it look as though the stars are twinkling. When astronomers use telescopes to take a picture of a celestial object through the atmosphere, the details are blurry. This blurriness prevented astronomers from realising the full potential of the powerful telescopes they built. It limited the view from the ground no matter how large the telescope. When astronomers want to study the skies by viewing other types of radiation, the atmosphere becomes even more of a problem because the Earth's atmosphere allows visible light and radiowaves to pass through but blocks out most other radiation, including X-rays and gamma rays.
Producing these space observatories, however, required significant advances in telescopes, instruments, computers, and, of course, the spacecraft used to launch them. Many of these technological advances came about as a direct result of the rivalry between the U.S. and the Soviet Union during the Cold War between World War II and the late 1980s. Scientists and engineers have created telescopes that can study the universe in many different types of light, and record details that could never be observed from Earth: space telescopes. Space telescopes and large, ground-based observatories work together to further our understanding of the universe. Space observatories have higher resolution and can look at tiny regions of the sky in great detail. Ground-based telescopes can collect more light with their colossal mirrors and be used to survey large portions of the sky. Despite recent strides made with adaptive optics on ground-based telescopes, space telescopes are still the best option for avoiding the blurriness caused by the atmosphere. NASA's Great Observatories programme constructed four orbiting telescopes - the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. Other space telescopes, like the James Webb Space Telescope, are being planned and built.
Finally, because space telescopes remain in orbit, fixing and upgrading them can be either difficult or impossible. When they eventually break down, they're gone forever. For now, though, space telescopes give humanity the clearest view of the universe. *** What makes a good telescope * Its light-collecting ability Faint objects are hard to see. Objects appear faint because they're far away, and/or because they glow dimly. The more light a telescope can collect, the better it can see faint objects. Large mirrors and lenses allow telescopes to collect more light. * Its resolution Resolution is the ability to see detail in an object. A telescope with high (good) resolution will be able to see two points of light as being separate from one another. A telescope with low resolution will blur the two points together into a single point of light. * Its magnifying power Except in the case of solar telescopes, magnification is the least important element of a research telescope. Magnification depends on focal length. As the magnification increases, the telescope focuses on a smaller piece of the sky. Most research telescopes are designed to operate at the smallest magnification possible, to examine a larger piece of the sky. The distance and details they see depends more on their light-collecting ability and resolution than their magnification. Solar telescopes, however, can rely on magnification because they don't have to look deep into space, see much of the sky, or gather much light to clearly view the Sun. * Instrument quality A modern research telescope is only as good as the cameras and other instruments that record and analyze the light that it captures. Instruments are judged by many factors, such as the quality of their images, how effectively they spread out light, and how much light they capture. Courtesy - Amazing Space |
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Radiation, such as that from infrared or ultraviolet rays, is partially
blocked. But, there was a solution - one that would have seemed beyond
belief to Galileo and surprised even the later day astronomers; with the
birth of space flight within reach, astronomers could break free of the
distorting and shielding effects of the Earth's atmosphere by placing
telescopes in space. 
Space telescopes have their drawbacks as well. They're much more
expensive to build and launch than ground-based observatories. Because
they must be launched into space, they can't be as large as ground-based
observatories. 
