Seeing through the Sun (April 9, 2002)
Using a technique recently developed, scientists have been generating
images of the far side of the Sun which are computed from sound
travel time analysis. These are based on observations by SOHO's
Michelson Doppler Imager (MDI). The images are whole-Sun maps of
magnetic activity that let us "see" sunspots many days before they
rotate into view. The second image shows the active regions of
intense magnetic activity in ultraviolet light (taken by the EIT 304Å
instrument) as they have just rotated into view. Coincidentally, a
large eruptive prominence can be seen blowing out from the Sun (lower
The farside images are maps of wave speed variations with locations of faster wave speed shown darker. These darker regions indicate locations where there is an accumulation of magnetic field on the far surface. The farside images can only be computed out to 45 degrees from the farside disk center as (un)seen from Earth. Intense magnetic fields around sunspots affect the transit times of sound waves bouncing from one side of the Sun to the other, variations that the MDI can detect and transform to reveal magnetic condensations (i.e, sunspots) on the hidden side of the Sun. This technique is called "helioseismic holography."
Previous Picks of the Week SOHO began its Weekly Pick some time after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.
If your institution would also like to receive the same Weekly Pick from us for display (usually in Photoshop or QuickTime format), please send your inquiry to firstname.lastname@example.org.