|P mode waves. Public domain image. SOURCE.|
Helioseismology is used to determine the inner structure of the Sun. The aforementioned wave oscillations are generated by convection, which is when cooler matter (in the case of stars, gas) moves downwards and the hottest matter moves upwards. The waves become visible because of the movement of gases, which appear as shifts of light along the spectrum (a process called redshift).
There are three types of waves: acoustic waves (which generate p modes), gravity waves (g modes), and surface gravity waves (f modes). The length of a wave oscillation is around five minutes, and modes have lifetimes from hours to months. These waves "resonate" in the Sun due to increases in the speed of sound, which then cause the wave to be reflected back toward the surface. The back-and-forth behavior creates what are called "standing waves".
By monitoring the waves, processes such as nuclear energy generation, energy flows, magnetic fields, and particle acceleration can be observed, and theories of stellar structure and evolution ("solar models") can be tested. Furthermore, helioseismology can show the temperature, density, composition, and motion in the interior of the Sun.
|The Sun, seen in UV light. Public domain image. SOURCE.|
Ilia Iankov Roussev
Ilia Roussev got a Master's Degree in Physics and Astronomy from Sofia University, Bulgaria, in 1995. In 1999 he studied solar events in Belfast, Northern Ireland at the Armagh Observatory. In 2001, he completed Ph.D. studies in Solar Physics and became a Research Fellow at the Center for Space Environment Modeling at the University of Michigan. He is currently a Associate Astronomer at the Institute for Astronomy in Hawaii, and a member of the American Geophysical Union, the Committee on Space Research, and the American Astronomical Society.
His research has included the solar atmosphere, solar magnetic fields, and waves and turbulence in space plasma.
Video of Ilia Roussev explaining helioseismology:
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-----The Golden Eagle