什麼是無線電和雷達天文學

通過測量天體發射或反射雷達波長的能量來研究天體。始於1931年，央斯基發現了來自地球外源的無線電波。1945年後，巨大的雷達圓盤天線、改進過的接收器和資料處理方法以及無線電干涉儀等，使得天文學家能夠研究更昏暗的源並得到更多的細節。無線電波能穿透太空中大多數的氣體和塵埃，比起光學觀察來，能給出銀河系中心清楚得多的圖像以及銀河系的結構。這樣就能研究我們的銀河系中的星際物質，發現以前不知道的宇宙天體（例如，脈衝星、類星體）。在雷達天文學中，無線電信號送往接近地球的天體或現象（例如，流星尾跡、月球、小行星、附近的行星），然後測出它們的回波，從而提供目標的距離及其表面結構的精確測量結果。由於雷達波能夠穿透濃密的雲層，所以它爲我們提供了金星表面的唯一地圖。在人類登上月球以前，對月球所作的無線電和雷達研究就已經揭示了月球的沙質表面。無線電觀察也提供了關於太陽的許多知識。亦請參閱radio telescope。

radio and radar astronomy

Study of celestial bodies by measuring the energy they emit or reflect at radio wavelengths. It began in 1931 with Karl Jansky's discovery of radio waves from an extraterrestrial source. After 1945, huge radar-dish antennas, improved receivers and data-processing methods, and radio interferometers let astronomers study fainter sources and obtain greater detail. Radio waves penetrate much of the gas and dust in space, giving a much clearer picture of the center and structure of the Milky Way than optical observation can. This has allowed detailed studies of the interstellar medium in our galaxy and the discovery of previously unknown cosmic objects (e.g., pulsars, quasars). In radar astronomy, radio signals are sent to near-earth bodies or phenomena (e.g., meteor trails, the moon, asteroids, nearby planets) and the reflections measured, providing precise measurement of the objects' distances and surface structure. Because radar waves can penetrate even dense clouds, they have provided our only maps of the surface of Venus. Radio and radar studies of the moon revealed its sandlike surface before landings were made. Radio observations have also contributed greatly to knowledge about the sun. See also radio telescope.