The Yohkoh satellite, launched in August 1991 by the Institute of Space and Astronautical Science of Japan, has been returning high‐energy solar data and images since early last fall. Designed to succeed earlier US and Japanese missions aimed at studying solar flares, Yohkoh (which means “Sunbeam” in Japanese) carries four instruments dedicated to monitoring the Sun's high‐energy radiation: A soft‐x‐ray (0.25‐4 keV) telescope, by mapping the emission from the hot coronal plasma, records the morphology of the magnetic fields that confine and control this plasma; a hard‐x‐ray (15–100 keV) telescope records bremsstrahlung emission from high‐energy electrons accelerated during a flare; and bent‐crystal Bragg and wide‐band spectrometers, which cover the spectral range from soft x rays to gamma rays, provide diagnostic data to aid in the analysis of the x‐ray images.

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