- 質問日時：2009/05/25 03:19
Stars emit electromagnetic radiation of different wavelengths. Radio waves have the longest wavelengths and gamma rays the shortest. Our eves are able to see visible light, somewhere in the middle.
Astronomers, the scientists who study the stars, use different sorts of telescopes to study these different wavelengths. In the 1950s, early radio telescopes were built to study the radio waves emitted by stars, using radar technology developed during the Second World War. But gamma rays and X-rays are absorbed by the Earth’s atmosphere, so NASA and other space agencies have launched a number of telescopes into space to study these rays.
A lot of the radiation emitted by ordinary stars is visible light, and astronomers use optical telescopes to study this. The first optical telescopes were built by Dutch spectacle makes around 1600, but the Italian scientist Galileo is famous for being the first astronomer to use a telescope. He studied the moon and discovered some of Jupiter’s moons in 1610. Modern telescopes use a concave mirror to capture light. The bigger the mirror, the more light the telescope can capture. Using a bigger telescope allows us to study fainter objects and see more detail. The history of the optical telescope is a history of a battle to build bigger telescopes with bigger mirrors.
The old English nursery rhyme that begins “Twinkle, twinkle, little star” actually describes an astronomer’s nightmare. Stars appear to twinkle, or shine brightly then weakly, because the light coming from them is disturbed as it travels through the Earth’s atmosphere. This also distorts their images in telescopes. There are two ways of overcoming this distortion. The first is to launch the telescope into space, above the Earth’s atmosphere, but that is very expensive. The Hubble Space Telescope was launched in 1990 to study visible and infrared light from above the Earth’s atmosphere. It had early problems, but a rescue operation by engineers in 1993 solved most of these and it has sent back to Earth some of the most fantastic images of the universe. It will operate until about 2010 and then be replaced by the James Webb Space Telescope, which is due to be launched in 2011.
The second solution is a new advanced technology called “adaptive optics” in which small moveable mirrors cancel out the distortions caused by the atmosphere. Early experiments have been successful and if this works, astronomers will be able to built Earth-based telescopes with enormous mirrors free from atmospheric distortion.
Some places on Earth are better than others for optical telescopes. Since they are used in the dark, they need clear skies away from cities or other artificial sources of light. Ideal places are between 20 and 40 degrees north or south of the equator on mountains higher than 3,500 meters. Some places where the best modern telescopes are located are Hawaii in the northern hemisphere and Chile in the southern hemisphere. Other ideal locations for telescopes in the future include Antarctica and the moon.
Astronomers these days never actually look through their telescopes. They use sensitive electronic detectors and computers to collect and analyze the light the telescopes pick up.
electromagnetic 「電磁気の」 gamma ray 「ガンマ線」 radio telescope 「電波望遠鏡」 distortion 「ゆがみ」 NASA （National Aeronautics and Space Administration） 「（米国の）航空宇宙局」 optical telescope 「光学望遠鏡」 Galileo （Galileo Galilei） 「ガリレオ・ガリレイ （1564-1642）」 Jupiter 「木星」 concave mirror 「凹面鏡」 Hubble Space Telescope 「ハッブル宇宙望遠鏡」 reflector telescope 「反射望遠鏡」 adaptive optics 「波面補償光学」