NASA/Marshall Solar Physics - Composite image
March 13, 1997
The image presented below is a composite of images taken by two separate telescopes aboard the Solar and Heliospheric Observatory (SOHO).
The inner, green image shows the sun in the light of strongly ionized iron (FE XII). While the sun is 99 percent hydrogen and helium, it is laced with metals and other elements that act like tracers in flowing water. Each element loses electrons at specific temperatures - the heavier the atom and the more electrons that are lost, the greater the temperature - so it is possible to see the sun (or other stars) at specific temperatures by taking pictures at wavelengths matching the energy required to ionize certain elements. This picture was taken by the Extreme-ultraviolet Imaging Telescope (EIT). EIT sees the sun in four wavelengths from 17.1 to 30.4 nanometers (nm; visible light spans 300 to 700 nm).
The images are taken in black and white; it is shown (to scale) here in green to contrast with the outer image taken by three telescopes making up the Large Angle and Spectrometric Coronal experiment (LASCO). LASCO blocks the blindingly bright disk of the sun and the intensely bright corona near the disk to reveal the faint outer corona and other features - like the cornal mass ejection (CME), traced by the green circle, suspected of having a role in the death of Telstar 401 - at distances up to 16 times the width of the sun. Previously, the corona had been seen only to 5 times the width of the sun.
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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack