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2289Re: Solar Activity Report for 8/4/04

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  • David
    Aug 6, 2004
      --- In methanehydrateclub@yahoogroups.com, "XK SAZ" <swezlex1@y...> wrote:
      > How do you tell it is holding together on the back side of the sun??
      >

      I just look at the SOHO satellite images on SPACEWEATHER.COM! Ohh,
      I'll bet you meant how can anybody tell, didn't you? ;-)

      The Solar and Heliospheric Observatory (SOHO) spacecraft has an
      instrument on board called the Michelson-Doppler Imager (MDI). The
      MDI can detect movements in the "surface" of the sun. Now obviously,
      the sun doesn't have a solid surface. When I say "surface," I really
      mean what we see as the visible surface, or the photosphere. Hold
      that thought.

      Did you know the sun makes noise? It does. The sun is a vibrating
      ball of sound waves. It isn't sound you could hear, though. The
      sound waves that travel though the sun have a period of around 5
      minutes. The sound we humans hear have a period much, much shorter
      than that. Still, though, it is sound, albeit it as very low
      frequency. Enter the field of study known as helioseismology. In
      much the same way that terrestrial scientists use the vibrations of
      earthquakes to probe the Earth's interior, solar scientists can do the
      same thing for the sun.

      Now obviously, you can't put any detection equipment on the sun, so
      how do they do that? By analyzing the movements in the photospere
      that the sound waves cause. Remember the MDI?

      Now for the sunspot part. It is known that intense magnetic fields on
      the sun, such as those associated with sunspots, cause variations in
      the way that sound waves travel through the sun. By analyzing
      photosphere movements with SOHO's MDI instrument, scientists can tell
      where the intense magnetic fields are on the other side of the sun.
      Where you find strong magnetic fields, you'll find sunspots.

      The technology isn't perfect, but it does a pretty good job of
      detecting large sunspots with strong magnetic fields. See this link
      for more info : http://www.spaceweather.com/glossary/farside.html
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