Yohkoh Soft X-Ray Telescope Images
Published Monthly in Solar-Geophysical Data Sep 1991-Dec 2001

To view and find out more information about downloading Yohkoh images, visit the YPOP (Yohkoh Public Outreach Project) film archives. Or, you may go directly to Lockheed's Soft-X-ray Telescope Page to see the archived Yohkoh images. Yohkoh images are also available each month for Sep 1991-Dec 2001 in print in the monthly publication Solar-Geophysical Data.

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The Yohkoh ("sunbeam") mission is a Japanese program designed to answer many questions in solar flare and coronal physics that have been raised by other highly successful missions. The United States and United Kingdom are participating partners in the mission. The Japanese Institute for Space and Astronautical Sciences (ISAS) provided overall program management, the launch vehicle, the mission instruments, and a Wide Band Spectrometer. The other primary instrument, a Soft X-ray Telescope, was prepared by the Lockheed Palo Alto Research Laboratory, under NASA support, in collaboration with the National Astronomical Observatory of Japan and the University of Tokyo.

Observing the solar disk with the soft x-ray telescope has many advantages over previous missions. It has become a vital tool for observing and attempting to understand solar flares. In August 1991 the Yokhoh satellite was launched. Since then it has proved itself to be an indispensable tool for charting flares with the highest level of detail over any other instrument yet. With the help of Yohkoh's soft x-ray telescope, researchers have been able to confirm Neupert's theory that after a "hard" or energetic flare occurs, a glow of "soft" or less energetic x-rays begin (Science News, Cowen, 1992). The primary objective of the Yohkoh mission is to obtain better information on high energy flare phenomena. The time phasing, and information on the detailed location of where in the sun's atmosphere the flare occurs are primary concerns, and the Yohkoh mission uncovers some of these mysteries. When a flare is not actually in progress, the soft x-ray telescope unveils many mysteries that may occur without the presence of flares.

ISAS bears full responsibility for YOHKOH operations. U.S. and U.K. investigators in residence at ISAS participate in mission operations and scientific analyses. With the approval of Professor Y. Ogawara, Yohkoh Program Manager, and the YOHKOH Science Committee, the Lockheed Palo Alto Research Laboratory is kindly providing daily digital SXT images for publication in SGD. The digital images 512x512 (5" pixels) or 256x256 (10" pixels) in size. They combine two exposures differing by a factor of 35 in duration and are printed with a logarithmic intensity scale to cope with the great range in intensity of the X-ray corona. The brightest features are typically more than 100,000 times brighter than the faintest. The mean wavelength of the pictures is about 20 angstroms. The images in SGD 1991-2001 were printed here at the National Geophysical Data Center on a dye sublimation printer, and published monthly in Solar-Geophysical Data. Currently the GOES Solar X-ray Imager (SXI) provides beautiful pictures of the Sun taken in the high energy X-ray wavelengths.