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How we see the far side of the Sun   SOHO's instruments include an imager, spectrometers, telescopes, coronagraphs and particle analysers. Using sound to 'look' through the Sun  Sun's far side (left) and visible side (right)seen by MDI, and showing sunspots 10486 and 10488 on the near side pointing toward us on Earth on 29 October 2003. Doing an ultrasound scan of the Sun!  Sun's visible side (left) and far side (right) seen by MDI, showing the sunspot regions two weeks later on 12 November on the side facing away from Earth. SOHO's SWAN instrument used in new method  SOHO's SWAN instrument sees 'Lyman-alpha' emissions, caused by ultraviolet rays interacting with hydrogen atoms, sweeping like a lighthouse beam across interplanetary gas beyond the Sun.
The Sun takes roughly four weeks to turn completely around on its axis, but active regions can appear and grow in only a few days. So until two years ago, no one had any way of telling when an active region might come 'around the corner' - perhaps blazing away with eruptions as soon as it appeared. If an active region can be detected in the middle of the far side it will appear on the eastern (left-hand) side of the visible disk about seven days later. Tools for space weather forecasts  Views from SOHO's SWAN instrument: the left sphere shows the far side of Sun, as seen from behind the Sun. So active regions which disappear from view on the right limb in the right sphere will appear on the left limb of the left sphere. Release date: 21 November 2003 |