Helioseismology is a relatively new topic in solar physics. Astronomers use a special type of spectrograph to measure the speed of surface gases on the sun, and make a 2-dimensional picture of how the speeds of various pieces of the sun change from minute to minute. It was discovered that these speeds do not change randomly, but of you were to 'stand' on a particular spot of the sun, you would find that the surface moves in and out with a speed that changes in a regular way throughout the course of seconds to minutes when you average the motions over regions with different areas. Mathematical analysis of these velocity versus time profiles across the sun shows that the sun is actually 'ringing' like some vast spherical bell and that at any moment the surface is tiles by a very regular checkerboard pattern of outward and inward-moving surface elements.
By studying the detailed patterning of these checkerboard surface elements and just how much they are moving, astronomers can probe deep inside the sun and explore the interior of the sun in a way that no other observation can do. Helioseismology is the only 'direct' way we can actually study the interior of the sun, its density, temperature and state of motion. This is why it is such an exciting technique.
All answers are provided by Dr. Sten Odenwald (Raytheon STX)
NASA IMAGE/POETRY Education and Public Outreach program.