At first astronomers used the visible light emitted by celestial bodies-and later the near-visible parts of the spectrum such as ultraviolet and infrared light-to deduce their distance, composition, size and other properties.
過去，研究人員利用天體發出的可見光，與接近可見光的紫外線、紅外線，推論天體的距離、成份、大小等性質。